I have over 10 characters with max account stats and one on PlayStation 4 as well. This guide consists of useful information I have found or researched of the many years I have played this game. It is the most up to date guide and has served me well during multiple playthroughs of mastering everything.

Please do like and favourite this guide, it took me a lot of time, and I'll continue to update this as I get more time. It'll mean a lot if you leave a comment as well. Thank you!
I recommend reading this entire section for tips, before skipping to the skill you want to upgrade.

The following skills are assisted by the following standing stone for xp gain:
Illusion, Conjuration, Destruction, Restoration, Alteration and Enchanting are all Mage skills.
Smithing, Heavy Armor, Block, Two-Handed, One-Handed and Archery are all Warrior skills.
Light Armor, Sneak, Lockpicking, Pickpocket, Speech and Alchemy are all Thief skills.

For each skill activate the respective guardian stone for more xp gain.

Lover stone - grants 15% more xp for skills
Easiest way of getting there is to go to Whiterun stables and tell the horserider to fast travel you to Markarth for 50(?) gold and then walk the rest.
Guardian stone - grants 20% more xp for skills
You probably passed this location on the start of your playthough, but if you didn't just backtrace from Whiterun and you'll find it.
Arkngthamz - Aetherium Crown location

I recommend doing the lost to ages quest line located at Arkngthamz and talking to the spirit Katria, and following the quest until you reach the forge and obtain the Aetherium crown.

Crafting this item requires:
1 x Aetherium Crest (acquired at end of Lost to Ages Questline)
2 x Dwarven Metal Ingot (purchasable from blacksmiths around Skyrim)
2 x Flawless Sapphire (looted from chests around Skyrim, also if you only have one you can duplicate the other using the method shown in the Enchanting skill section)
2 x Gold Ingot (purchasable from blacksmiths around Skyrim)

The crown gives you the ability to have 2 standing stones active to help with xp gain. If you are levelling a warrior skill, you can get lover stone and warrior standing stone.

There also exists a glitch to obtain all 3 guardian stones and lover stone if you wish to use cheats. This video will explain how to accomplish it.

It is also advised you get a magika gear for casting mage skills. Or do the Dragonborn DLC to get the black book that lets you have infinite magicka and as long as you continue to hold the spell activation down the 30 second window becomes infinite for infinite magicka usage.

For Magicka and Stamina regen skill I recommend use waiting to replenish your respective stat to allow you to quickly cast/swing again, instead of manually waiting in real time.

The reason this skill is first, is because, if you are going to unlock every skill to 100, this is the one you need to look out for, since its not really afkable.

This is the only skill and possibly Archery I recommend using trainers found around skyrim to level up.

Level 1 - 90
Everytime you level up in skyrim go to Riften and go to the Ragged Flagon and find Vex. She can train you in Lockpicking for gold. If you need money you can use this guide below which is easily accessible early game.

Alternate Level 1 - 90
Duplicate as many lockpicks as possible (tutorial in enchanting section), and go around skyrim opening as many difficult locks as possible to yeild more xp. I recommend upgrading this skill tree to make life easier. You can try using the level 90 - 95 strategy and once you've opened the master and expert locks you can wait 10 in game days to reset all picked locks.

During the thieves guild quest you unlock an unbreakable lockpick which saves u duplicating 1000s of lockpicks, but duplicating items are exponential and not too difficult to set up.

Level 90 - 95
Go to Dwemer Museum in Markarth and sneak and lockpick all the Master and Expert locks. Duplicate lockpicks if you need them (guide found in Enchanting guide section). Also obtain some fortify lockpicking armor if you are struggling, along with leveling skill tree to assist you. If you run out of locks to pick wait 10 in game days to reset dwemer museum locks.

Level 95+
You can continue lockpicking in Dwemer Musuem but if you are really struggling I recommend obtaining the skill books:

Advances in Lockpicking (The Ragged Flagon - Cistern, on a barrel in the north east room.)
The Wolf Queen, Book I (bought from Urag gro-Shub in The Arcanaeum)
Proper Lock Design (Faldar's Tooth – at the top of the tower on a table)
The Locked Room
Surfeit of Thieves (Mistveil Keep in Riften, Jarl's Chambers, in the northern bedroom on the left nightstand)

Above locations were found from ElderScrolls wiki.

Alternate "AFK" Leveling Strategy:
I mentioned earlier you can duplicate lockpicks as shown in the Enchanting skill section but you can use this exponential growth in lockpicks to intentionally fail the lockpick for an afkable option. Since in this game you get xp for breaking your lockpick.

Level 1 - 25
Equip your Magicka gear and find Drevis Neloren of the College of Winterhold to obtain Clairvoyance spell. You'd tend to find him at either the Hall of Countenance (where he sleeps from 12 AM until morning) or in The Arcanaeum.

Level 25+
Obtain Muffle from Drevis Neloren after reaching level 25. You may need to wait 48 hours if his shops doesn't have the tome yet. Then cast the spell in a crowded area, my recommendation in whiterun in the market area. Dual cast this spell in each hand for more time efficient xp gain.

Level 1+
Buy the tome Soul Trap from Farengar Secret-Fire at whiterun who is in Dragon's reach. After obtaining the spell go kill a high level enemy on find a dead animal in the wild and dual cast soul trap on the dead body repeatedly. You'll gain more xp if you cast it on an higher level enemy.

Please note to do the following method the "Unofficial Skyrim Special Edition Patch" removes the ability to repeatedly cast soul trap on a dead being. Credit to Spirit3057.
Alternatively you can use Bound bow which can be acquired from Farengar Secret-Fire at whiterun who is in Dragon's reach, and grind in unison with Archery skill.

I recommend progressing darkbrotherhood quest line to unlock Shadowmere, but if you don't want to get Shadowmere you can use a horse from any of the stables around the map. It helps lowering difficulty to Novice in order to output more damage onto Shadowmere since he has such high health regen.

Level 1 - 25
Dual cast Flames onto the horse

Level 25 - 75
Dual cast Firebolt which Faralda can give at College of Winterhold when your first enter, if not you can obtain from her when you meet her in Hall of Countenance.

Level 75+
Cast Wall of Flames on Shadowmere for insane xp gain

or

Travel to Hob's Fall Cave to obtain Unbound Storms tome and cast outside of Riften to not agro any guards then fast travel to opposite corner of the map.

Seek Heavy and Light Armor section for methodology.
All spells below are obtain by Colette Marence at second floor of the Hall of Countenance in College of Winterhold.

Level 1 - 25
Cast Healing

Level 25 - 50
Cast Fast Healing

Level 50 - 75
Cast Close Wounds

Level 75+
Cast Grand Healing

Obtain Telekinesis from Red Water Den and when you are locked up in a prison cell you'll get an telekinesis spell tome.

Level 1+
Go to Riften and pick up an dropped item with telekinesis then open map and fast travel to your furthest away location. Upon arrival you would've gained all levels.

Obtain as many filled grand souls gems from merchants around the map, court wizard Farengar Secret-Fire in Dragons Reach, Whiterun.

Then go to Dawnstar and steal weapons and armour to enchant

After you've obtained as many weapons and armour, duplicate as many filled grand soul gems as possible in Whiterun.
1. Stand by main Entrance in whiterun with your follower next to you
2. Drop as many of your grand soul gems 1 at a time on the floor
3. Make your follower pick up the items on the floor
4. Travel through the guards gate of whiterun into the open world
5. Fast travel back into whiterun
6. The items will be both on the floor and inside your followers inventory

You can use all the soul gems along with the weapons and armour and enchant as much as possible.

Smithing XP is based off of the item's value of which you are crafting so please do not spam gold rings since they aren't valuable. Just craft whatever valuable item you can afford with your materials.

Alternatively if you don't mind using OP tech you can try the below.
Use the restoration loop to create an OP smithing potion which is made up of:
Blisterwort
Glowing Mushroom
Sabre Cat Tooth
Spriggan Sap

Then consume the potion and improve your sword at a grindstone found at most forges in skyrim. The higher the smithing potion the more levels you'll get.

1. Craft the strongest armour you can make
2. Go to a location with Giants/enemies
3. Let them attack you while you use your strongest restoration spell, run away if you are going to die, adjust your difficulty level if they don't do enough damage or if they do too much damage.

You can gain xp faster if the difficulty is harder, around level 75+ I used master difficulty with grand healing spell with dragonbone armour.

1. Craft the strongest shield you can make
2. Go to a location with Giants/enemies
3. Let them attack you while you block the attacks, run away if you are going to die, adjust your difficulty level if they don't do enough damage or if they do too much damage. You can use healing between hits if you are time it well enough against giants and mammoths.

You can get xp faster the harder the difficulty is.

Unlock Elemental Fury Shout from the word wall at the following locations:
Dragontooth Crater
Shriekwind Bastion
Statue to Meridia

And obtain shadowmere from darkbrotherhood questline or buy a horse from many of the stables around skyrim.

TIP: Change difficulty to adept against shadowmere for more damage output since xp gain is based on damage dealt, and avoid leveling up skills that increase the weapon classes damage such as Barbarian "Two-Handed weapons do 20% more damage".

1. use the elemental fury shout
2. attack horse with greatsword
3. wait 1h
4. repeat

Unlock Elemental Fury Shout from the word wall at the following locations:
Dragontooth Crater
Shriekwind Bastion
Statue to Meridia

And obtain shadowmere from darkbrotherhood questline or buy a horse from many of the stables around skyrim.

TIP: Change difficulty to adept against shadowmere for more damage output since xp gain is based on damage dealt, and avoid leveling up skills that increase the weapon classes damage such as Armsman "One-handed weapons do 20% more damage (+20% per additional rank)".

1. use the elemental fury shout
2. attack horse with sword and mace in each hand
3. wait 1h
4. repeat

Another method which will also level up sneak is to go to High Hrothgar where the graybeards pray and sneak up behind them with dual wield daggers on Legendary difficulty, and go ham on backstabbing them while sneaking.
Try to output as much damage as possible so investing in the skill Armsman and Bladesman will help alot.
Please be sure to quicksave (f5 button) incase they get up and try to attack you, that way you won't have to restart the process. Credit to Kiwi in the comments below.

If you need more arrows try duplicating them as seen in the Enchanting guide above.

Also please be sure to save every 2-5 minutes incase they graybeards catch you so you can revert the save to before they got angry.

Level 1 - 94
Shoot arrows at Graybeards in High Hrothgar while they aren't looking in the main entrance. Sneak to try to level sneak at the same time and remain hidden too. Use strongest bow and put the difficulty to adept to deal more damage. Please make sure to quicksave (f5 button) every 2 or 5 minutes so you don't lose progress when they attack and kill you.

Level 94+
Go to Angi's Camp and complete her tasks and she will train you to level 100 faster than manually grinding final few levels. Please note you can only do this once so its recommended you don't waste her training you on early levels which require less xp to level up.

Please note if you are running "Unofficial Skyrim Special Edition Patch" you may want to level conjuration at the same time by using Bound Bow, which can be acquired from Farengar Secret-Fire at whiterun who is in Dragon's reach. This was you can also passively level Conjuration.

1. Craft the dragonscale armour
2. (optional) enchant the armour with fortify health or fortify light armor
3. Go to a location with Giants/enemies
4. Let them attack you while you use your strongest restoration spell, run away if you are going to die, adjust your difficulty level if they don't do enough damage or if they do too much damage.

You can gain xp faster if the difficulty is harder, around level 75+ I used master difficulty with grand healing.

It's recommended you do this first partially with Archery skill in order to passively do as much as possible if maxing all skills.

Then level up remaining xp required by sneak walking upstairs in Dragons Reach, Whiterun into a safe corner. This is because xp is given based on sneaking near populated areas and remaining hidden at the same time. Note a guard does patrol upstairs so try to position yourself so you are not seen by them.

I found this video helpful below

For an Alternate method which also levels up One-Handed check out the One-Handed Section of this guide

1. Get arrested in Riften to go the the jail
2. Escape your cell using alteration/destruction magic or lockpicking out
3. Get only your money back from your belongings chest from the key from the guard
4. Pickpocket 200 coins into Sibbi Blackbriar then out of his pocket
5. Repeat step 4
6. Overtime slowly increase amount stolen/deposited but don't increase it to more than 1200 or you can not steal from Sibbi Blackbriar anymore

All the ingredients below can be bought from Arcadia's Cauldron, you can refresh her inventory by waiting 48 hours.
Use the restoration glitch and create a fortify enchanting potion.

For the glitch fortify enchanting potion you need at least 3:

Ancestor Moth Wing
Blue Butterfly Wing
Chaurus Hunter Antennae
Hagraven Claw
Snowberries
Spawn Ash
Spriggan Sap

Then after you've made the overpowered potion drink it and enchant fortify alchemy onto your gear.

After equipping your new fortify alchemy gear make as many potions containing the following ingredients:

Giant's Toe
Creep Cluster
Wheat

Duplicate the ingredients above before hand (duplication tutorial in Enchanting guide) to help with the process.

You can level speech easily by selling high value items.
It is best to do this skill after doing the Alchemy skill by selling the giant's toe, creep cluster and wheat potion to merchants found across skyrim.

Duplicate the potions (guide in Enchanting guide section) if you need more potions to sell to Merchants.

This guide was kinda rushed and may not make sense at certain points, the original plan for this guide was barebones.
https://imgur.com/a/kfBIfQM <-screenshot of my notepad file

Please do comment below if you need assistance or if i made any mistakes.
Thanks for reading Dragonborn.

“What is better? To be born good, or to overcome your evil nature through great effort?” ~ Paarthurnax