The idea between choosing your class is that you want to rotate through them regularly, typically after you are able to beat a boss with one, before moving onto the next.

Each class receives the following bonuses after defeating a boss, which upgrades all your characters:

Paladin - Armor
Ranger - Attack Power
Sorcerer - Mana Regen
Warlock - Resistance
Thief - Gold Bonus%
Priest - HP Regen
Wizard - Skill Power
Gladiator - Primary Crit Damage
Witch Hunter - Skill Crit Damage

More info can be found on the game's wiki page (under "Guild Hall"), but tracking the above bonuses is paramount and should be done regularly. Beat a boss, switch classes.

On your first game, try Ranger first (it's the easiest). Rotate through classes once you beat each boss.

Build Priority:

On the Prowl 1
Grasping Roots 1/Bow Shot 2
Marked Prey 1
Twinned Arrows to max when you can
Powershot 1
Bow Shot to max
On the Prowl to max
Marked Prey to max
Decide if you want to upgrade Flurry of Arrows for its damage, or if you'd rather have more uses of Powershot with your mana capacity.
Grasping Roots to max

Skills:

Bow Shot - Piercing arrows is important, as well as reduced movement speed while firing. You also fire slower while moving.
Flurry of Arrows - Helps you clear rooms if you run into the middle. I like this better left not ranked up so that it can be used cheaply and more often with On the Prowl. Note that Bow Shot increases the damage of Flurry as well, clearly making Bow Shot a priority. Does Physical Damage.
Grasping Roots - the ranger's panic button. The armor reduction makes this a useful offensive tool as well.
Powershot - Powerful corridor clearing ability, great for using up spare mana. Keep it at rank 1 for a long time, it'll do the job.
On the Prowl (passive) - +25% movement speed and increased evasion whenever you use any skill. Valuable.
Marked Prey (passive) - crits for your primary attack and 2.5 second marks for your party members (or potentially from flurry).
Twinned Arrows (passive) - big damage spike that homes in on more enemies

Build Priority:

Shield 1
Lay on Hands 1
Flames of Devotion 1
Flames of Devotion 2/Stunning Blows 1
Whirlwind 1
Shield/Lay on Hands/Sword to max (Shield tends to be more important than Sword here)
Stunning Blows to max
Whirlwind to max


Skills:

Sword - Primary attack, higher ranks mean more damage and bigger arc. Not important.
Charge - More ranks mean more range, but I've never needed more range and the rest doesn't matter.
Lay on Hands - Mana for heals, and it even heals party members as icing on the cake. Very important.
Whirlwind - Primary damage dealing ability, but I feel like I've never needed it. When you attack groups, you'll be using your sword, combo, and to a lesser extent charge.
Shield (passive) - The arc is very important, you will get surrounded a lot.
Stunning Blows (passive) - It's only ever 2.5 seconds, and you won't notice it unless you're fighting a miniboss, but disabling an enemy from attacking you is always welcome. Doesn't work against bosses at all, which is where you'll usually die, so keep that in mind.
Flames of Devotion (passive) - This will be the brunt of your damage, and the second each stack lasts is more significant than it seems since you're often killing groups with combo. Stacks count down from your maximum, so you'll regularly be at maximum stacks. Importantly, this is Magical damage, not Physical damage.

Build Priority:

Frost Shard 2
Frost Nova 1
Optionally Biting Chill 1
Optionally Orb of Winter 1
Shatter/Frost Shard to max
Frost Nova/Biting Chill to max
Orb of Winter to max
Comet/Ice Barrier to max

Skills:

Frost Shard - S tier. More ricochets makes your primary very strong. You will never regret ranking this up as high as you can.
Comet - Garbage. If you're really lucky it will go where you want it to.
Frost Nova - A tier. This will be your primary skill. Low mana cost, good damage, the frost balls seem to target enemies, though I can't tell if this is just regular coincidence.
Orb of Winter - B tier. This is a nice room-clearing ability. Its big weakness is it eats almost all your mana, severely limiting its use. You'll usually want to use Frost Nova multiple times instead for the same effect.
Biting Chill (passive) - Free slows and freezes is nice but not super noticeable at low levels.
Ice Barrier (passive) - Sounds so worthless that I haven't tested it. You're usually firing at range, the barrier doesn't last long, and it doesn't even block a full single hit - only a percentage of it, even at the highest level.
Shatter (passive) - bonus burst damage. the tooltip says enemies killed when frozen shatter, but I found enemies shattering all the time, even when just chilled. Big damage bump.

Build Priority:

Extended Domain should be maxxed as long as you can handle,
Soul Cleaver 1
Summon Gargoyle 1
Eye of the Storm 1 when you can
Stormlash 1 when you can
Stormlash 2 when you can
Soul Dagger to max
Summon Gargoyle/Soul Cleaver to max
Lightning Bolt/Eye of the Storm to max

Skills:

Soul Dagger - Fast firing attack that does magical damage but upgrades based on Weapon Damage rather than Skill Damage. You can make do with 1 rank of this for a while.
Lightning Bolt - It's fine but I feel like gargoyle does more overall damage. Unlike gargoyle, you don't have to put yourself in harm's way for this, so it can be a good for a quick low mana cost burst at range.
Summon Gargoyle - Gargoyles synergise with other gargoyles and eye of the storm, meaning mass sustained damage.
Eye of the Storm - Untested. Note that one of these is about the same cost as 2 gargoyles.
Extended Domain (passive) - By far the most important unlock the warlock has. More range means more damage on all your unlocks (including Soul Dagger), for the price of one unlock per rank.
Soul Cleaver (passive) - Also important, but 1 rank is enough for a while.
Stormlash (passive) - More damage. I can't tell if this has a bounce limit.

Build priority:

Combustion 1
Blast Wave 1
Flame Shield 1
Scorched Earth to max
Fireball/Combustion to max
Blast Wave/Fire Breath to max
Flame Shield to max
Meteor Shower to max

Skills:

Fireball - Primary attack with an AoE.
Fire Breath - Holding right click roots you in place and drops fire and burning status on everything. Great to do quickly and kite your enemies back to quickly get combo.
Blast Wave - Damage, slow and confusion to everything around you, and destroys most projectiles. This is great, but best used in synergy with Flame Shield.
Meteor Shower - Not good at low levels, especially against bosses. You will be rooted in place for a second too long and probably get hit and/or killed. If you're lucky, the burst damage might be worth it.
Combustion - Important passive puts burning on everything you hit, including your primary attack.
Flame Shield - The important part of this is that you get a free Blast Wave anytime you get hit. As a secondary effect, it blocks some damage. This Blast Wave is your current level of Blast Wave, so upgrade that instead of this after your first rank.
Scorched Earth - Valuable. Leaves burning damage areas on anything you hit with Fireball, Blast Wave or Meteor Shower (NOT Fire Breath).

Plays similarly to the Ranger, but less range and more utility.

Build Priority:

Repeater Crossbow 2
Fanatic Zeal 1
Witch's Pyre 1 or Branding Ward 1 (Witch's Pyre is better, but Branding Ward can do a similar albeit riskier job while you wait for skill points to come in)
any of the above abilities except Branding Ward to max, or up until you can unlock Searing Torch 1 and 2
Branding Ward to max
A Murder of Crows 1
A Murder of Crows to max
Flaming Hounds to max, if you want and if you can afford the mana/mana regen - you want this to be low mana cost for Fanatic Zeal/Searing Torch use


Skills:

Repeater Crossbow - Primary attack. Piercing is very nice, even with the damage reduction.
Flaming Hounds - It's OK, but doesn't do much more than just firing your primary attack. Has synergy with Fanatic Zeal with its lower mana cost, but most of the time you won't care unless you're dropping a Witch Pyre instead.
Branding Ward - Nicely supplements your primary attack, but you do have to move to a choke point to drop this.
Witch Pyre - Taunts enemies to attack it, allowing you a lot of extra breathing room while laying down some damage.
Fanatic Zeal (passive) - Kind of hard to notice, but theoretically more crit chance like this is a significant damage boost against high hit point targets like bosses.
A Murder of Crows (passive) - Free damage that never does anything unless you get hit. Hard to tell how much damage this actually does and it doesn't say how long it lasts, but neither are significant at low levels. The 10 second cooldown makes it worse.
Searing Torch - bonus long range burst damage with fire (about 1/3 of the screen) when you use a skill. Unless you use flaming hounds a lot, you probably won't get much out of this.

Plays like the Paladin but more damage/movement focused and uses evasion for defense instead of a shield.

Build Priority:

Sidestep 1
Slice and Dice 1
Twin Daggers 2
Smoke Bomb 1/Grappling Hook 1 (both optional)
Sidestep/Slice and Dice to max, balance these
Twin Daggers to max
Grappling Hook/Smoke Bomb/Vicious cuts to max

Between Sidestep, Slice and Dice and Twin Daggers - prioritise what you feel like you need more of during your fights.
If you need more defense, upgrade Sidestep.
If you need more damage, upgrade Slice and Dice.
If you need more movement speed, upgrade Twin Daggers.

Skills:

Twin Daggers - You'll want to attack a lot all the time and you won't want to lose movement speed while doing so, making upgrades on your fast primary attack important.
Throwing Knives - Piercing is nice, but the problem is you're throwing your knives out in an arc. Most of the time you just won't need this.
Grappling Hook - Better for utility than anything else. Potentially good for escapes if you can get used to the range so that you don't accidentally misfire and expect to be pulled but instead nothing happens.
Smoke Bomb - Great panic button and the evasion increases with every rank are very nice.
Sidestep (passive) - Evasion is the thief's bread and butter. This would be nice even if it didn't also include a secondary guaranteed evasion effect.
Slice and Dice (passive) - Works similarly to combo, drastically increasing ongoing damage. The 2.5 second expiration never increases, meaning slightly diminishing returns unless you're great at sticking to targets.
Vicious Cuts (passive) - Works best on targets with large health pools and near full health.

Like Thief but with less evasion and lots of melee button mashing. It's not a bad idea to rebind mousewheel-down to attack.

Build Priority:

Planned Attack 1
Trident 2
Pit Fighters 1 (then upgrade this to max when your mana capacity can handle it)
Spinning Gladius 1
Riposte 1
Trident/Riposte to max
Planned Attack to max
Strength in Numbers to max
Crippling Net to max.
Spinning Gladius to max

Skills:

Trident - The only class where you have to button mash and listen to a shovel hitting pavement repeatedly. Only triggers when you button mash (otherwise you attack at a significantly slower speed, albeit at the Trident level of damage).
Crippling Net - Not worth it at low levels.
Spinning Gladius - Decent ranged attack but can be a little tricky to aim it where you want it to stop. Not completely unintuitive though, and has nice damage bonuses per rank.
Pit Fighters - Create room-clearing extra players.
Planned Attack (passive) - Guaranteed critical hits. Separate stacks to Trident - one attack will take a stack of Trident and a stack of Planned Attack. Only triggers when you button mash.
Riposte (passive) - Its redeeming feature is that if it blocks an attack, you get a stack of Trident back which means more damage, but it's within a 0.2 second window. The blocking percentage refreshes as fast as you can attack, which is all the time with Gladiator, meaning near permanent damage reduction while you're in combat.
Strength In Numbers (passive) - Just a buff for your strongest skills.

Build Priority:

Smite 2/Consecrated Ground 1
Remedy 1
Celestial Orbs to max
Smite 3/Remedy 2
Smite to max/Remedy to max/Holy Light to max
Aura of Purification to max

You can pick up Divine Protection at any time (probably after taking Celestial Orbs 2), but ONLY if you are able to max it all at once due to how permanently mana costly it is.

Skills:

Smite/Consecrated Ground - this is how you'll start off attacking enemies, and if both you and the enemies are within the area, you'll also be able to heal yourself. Get in the habit of running backwards out of the consecrated ground while attacking as enemies start entering it, otherwise you'll take damage.
Holy Light - mainly used for manually targeting Celestial Orbs, meaning you don't have to upgrade it until much later. Unlike similar abilities that other classes have, you can move at normal speed while firing it. If you're playing in multiplayer, you may need to upgrade this earlier for bigger heals, as this is how you'll usually heal them. You cannot heal yourself with Holy Light, unless you also use it with Consecrated Ground. Be careful with upgrades, as the mana cost will rise significantly considering how fast this fires.
Remedy - If you feel like you're not getting enough heals, upgrade this.
Celestial Orbs - very important for the Priest, allowing you to run through enemies and it will usually do the work firing automatically for you.
Divine Protection - frankly this feels broken in a bad way without a way to temporarily disable it.