I tried to write the guide with as little spoilers as possible, but please keep in mind that mild spoilers will be in this guide since they're needed to explain how to get plot related achievements. Read at your own risk!

Every Quest in the game seems to have 2 outcome versions, simply getting the outcome gives you an achievements. The majority of achievements in the game are earned that way. There are 15 quests in the questbook, yet the final one is handled in the endings which have different achievements, so 14 Quest with 2 Outcomes gives you 28 achievement already by simply playing the game. You can check which achievements you already have and simply do the exact opposite in your next playthrough to get all of them.

• Let's call them outcome achievements

Some other achievements are linked to the main story and cannot be missed.

• Let's call them plot achievements

Some others are linked to the 4 different ending (good, mid, bad & hidden).
Since the hidden ending has very similar requirements as the bad ending, you can do both in one playthrough if you're playing optimal, meaning to get every achievement you have to play through the game at least three times for 100%.

• Let's call them ending achievements

Apart from that, some achievements require you to do specific things over the course of the game, which are overall rather easy to do.

• Let's call them objective achievements

First step
You get this achievement by simply making your first drink, this is not missable

Still in training
You get this by giving an adventurer a wrong drink. E.g. if someone requests a drink which has Dexterity as the highest stat, make one which does not have dexterity at all in it


Eating mistakes away
Use Andu, the small little dragon in the drink mixing nook and pour something from the mug into him to undo a step for the first time.


So cute!
Pet Andu, simply by clicking on him and enjoy the animation <3


Onwards!
Combine 3 rumors into a quest at the end of a day for the first time. Since that is needed for the progression, this achievement is also not missable


Some spice to the table
Add an infusion to a drink. This is needed for quests, since mixing drinks for them have specific requirements. So this achievement also can not be missed.


Enough...
This achievment is a bit more uncommon, but still easy to get. When mixing a drink for a quest, you have to make a specific recipe that fits and the game wont let you do anything completely different. For this achievement to trigger, you have to do it wrong on purpose. Do this 3 times in a row and poor Andu will hide in the bucket. For this to trigger, mix a wrong drink (e.g. wrong stats, wrong infusion or nor infusion when needed, etc.) complete it and click on the bell. Then remove at least a step, mix a wrong drink again and click the bell again. After clicking the bell for the third time, the achievement will trigger.


WOW
When making a drink called Sparkling Nebula, there is a chance of Andu looking especially happy since he seems to like it. Whenever that happens, the achievement will trigger.


Drink master
For this you have to mix every drink in the game at least once. While the achievement counts globally, this has to be done in one playthrough, saving and loading an older save to do one drink over and over again does not work. Saving and loading is fine, just not an older save since that would undo other drinks you've already mixed in the tracker. To be sure which drink you've already made or not you'd have to keep track of it yourself, since the game wont show it to you directly.


Some sparkle on top
The same as Drink master, just for infusions. Use every infusion at least once - again keep in mind to do it in one playthrough


Best tavern ever
You get this achievement automatically after you got every other achievement in the game

See the stars
To get this achievement you have to simply finish Act 1


Blup blup
You get this for finishing Act 2


Oh-Oh
This is earned for finishing Act 3


Hello old friend
You get this achievement for talking with the old friend on chapter XXII, 32th of the Astral Moon


Mysterious letter
For this you have to open the letter Kyle brings you in chapter IV, 60th of the wake. However the Innkeeper does not want to open the letter right away. This happens at a fixed point in the story much later, in chapter XIII, 17th of the Astral Moon


It's Renu
You get this once you receive your other familiar, who you can then see in the background right inside your tavern. This happens no matter which quests or outcomes you do, always in chapter XII, 10th of the Astral Moon

Party time
Get the good ending. For this to happen, you have to get the good for the majority of quests in the playthrough. You dont have to do everything perfectly, but about 80% or so need to be right. More details on which quest outcomes count as good or bad below.


All's well that endds well
Get the normal ending. For this you need to get the good outcome for some quests and the bad outcome for others. It does not matter which specific quest you do in which way, it only overall has to be balanced. When playing through it casually, this is normale the default ending a lot of players will reach. More details on which quest outcomes count as good or bad below.


The end
Get the bad ending. For this you need to do the opposite as for the good ending. The majority of quests needs to be solved the bad way. Again, not everything has to be done this way, but the majority.


The end... together?
This is the hidden ending in the game and is triggered in a specific dialogue with Quasar on chapter XXII, 32th of the Astral Moon. Without spoiling any details, you get a new dialogue option depending on your decisions throughout the game. This is by far the most complex achievement.
Marked as Spoiler:

Up until the point of this dialogue with him, you have to:

• A Werewolf on Detours Quest: make a drink that has a focus on Dexterity
  
• Hey There Evelynn: make a drink that has a focus on Strength
  
• Until Sunrise: make a drink that has a focus on Defence
  
• Twinkle, Twinkle Deadly Stars: make a drink that has a focus on Defence
  
• A scandal in Zoford: make a drink that has a focus on Strength
  
• Fatal company: make a drink that has a focus on Intelligence
  
• Raiders of the Lost Archives: make a drink that has a focus on Strength
  
• The vegan dead: make a drink that has a focus on Dexterity
  
• Mission magically possible: make a drink that has a focus on Strength
  
• Heir of Dragon Fire: make a drink that has a focus on Dexterity

Once the dialogue with Quasar starts, you have to pick specific negative dialogue choices:

• When he asks if you manipulate people, tell him: "Exactly, you know me too well."
  
• When he asks how you're doing after he tells you his intentions, tell him: "I'm full of hope for a better tomorrow" and are not worried about a potential end of the world.
  
• When he talks to you about the stars, tell him "It meant everything to me"

If you've done everything correctly, near the end of the dialogue he asks you if you want to join him. Normally the Innkeeper answers with no, but this time you should have a dialogue option to say "That sounds beautiful. Like a dream worth dreaming." which triggers the hidden ending path.

Additional hint: A lot of the quest outcomes you have to do to get this ending are also counted as the bad version. Meaning you can save right before the choice and load later to continue as normal to get the bad ending + achievement in the same playthrough!

This is a list of all quests and which stats are needed for the quest related drink mixing.

• Take aim - Dexterity related drink for A Werewolf on detours
  
• Diplomacy is key - Charisma related drink for A Werewolf on detours
  
• Rogue - Strength related drink for Hey There Evelynn!
  
• Shadow - Dexterity related drink for Hey There Evelynn!
  
• The beast - Defence related drink for Until Sunrise
  
• Puppet master - Intelligence related drink for Until Sunrise
  
• Gently giant - Intelligence related drink for Twinkle, Twinkle - Deadly Stars
  
• Beatuy and sadness - Defence related drink for Twinkle, Twinkle - Deadly Stars
  
• Cold case - Strength related drink for A Scandal in Zoford
  
• Case closed - Charisma related drink for A Scandal in Zoford
  
• Distract and run - Intelligence related drink for Fatal Company
  
• Hero's journey - Defence related drink for Fatal Company
  
• Camouflage - Intelligence related drink for The Lagoon of Tranquility
  
• A lullaby - Charisma related drink for The Lagoon of Tranquility
  
• Archiving - Strength related drink for Raiders of the Lost Archives
  
• Ever blooming - Defence related drink for Raiders of the Lost Archives
  
• Katallage - Charisma related drink for The Parent Trap
  
• Katharsis - Strength related drink for The Parent Trap
  
• Burn out - Dexterity related drink for The Vegan Dead
  
• Unionize - Charisma related drink for The Vegan Dead
  
• Boom! - Strength related drink for Mission: Magically Possible
  
• From rags to riches - Intelligence related drink for Mission: Magically Possible
  
• First Star - Defence related drink for The Twilight Chase
  
• Last Dawn - Dexterity related drink for The Twilight Chase
  
• Lights out - Dexterity related drink for Heir of Dragon Fire
  
• Guivre - Intelligence related drink for Heir of Dragon Fire
  
• Army of friendship - Dexterity related drink for The Dead Parade
  
• Joint forces - Charisma related drink for The Dead Parade

This is a simple quest list of which outcomes are counted as good and which as the bad version:

• A Werewolf on detours - Charisma version counts as the good outcome
  
• Hey There Evelynn! - Dexterity version counts as the good outcome
  
• Until Sunrise - Intelligence version counts as the good outcome
  
• Twinkle, Twinkle - Deadly Stars - Intelligence version counts as the good outcome
  
• A Scandal in Zoford - Charisma version counts as the good outcome
  
• Fatal Company - Defence version counts as the good outcome
  
• The Lagoon of Tranquility - Charisma counts as the good version
  
• Raiders of the Lost Archives - Defence counts as the good version
  
• The Parent Trap - Both count as good outcomes!
  
• The Vegan Dead - Charisma counts as the good version
  
• Mission: Magically Possible - Intelligence counts as the good version
  
• The Twilight Chase - Both count as bad outcomes!
  
• Heir of Dragon Fire - Intelligence counts as good outcomes
  
• The Dead Parade - Charisma counts as good outcomes

With this you hopefully should know everything you need, if you have any questions just throw them in the comments ^^