It's recommended you do separate playthroughs for all the achievements. Don't worry though, the second is very short.

Standard playthrough with several things to note:

• 5 achievements require you to solve a puzzle in the first attempt. PROTOTYPE303 has a guide here that covers puzzle solutions.
  
• Look and talk to everyone, there are two achievements for this. With one exception:
  
• Do not talk to Merlin unless necessary. You only need to visit him 4 times.

Done right, you will unlock 22 achievements and only have two left for your second playthrough.

Turn off autosaves and play through the entire game without saves. This isn't nearly as bad as it sounds, and you should be familiar with the game now after the first playthrough.
It takes around 45mins if you skip dialogue and cutscenes.

These achievements are ones you should be aware of before starting the game.

The Observer
You made sure to examine and look at many things throughout your tale!

Examine (right clicking) on a large number of items. This unlocked for me during Thor's section of the story, so there's no need to pixel hunt for every examinable item. Though I recommend you examine everything along the way as there won't be enough items left if you leave it too late in the story.
It seems like you need ~200 items examined and they all need to be different, so you can't keep examining the same item to get the achievement.

The achievement unlocks immediately upon examining enough items.



Ker'aooc The Wizard
You only used Merlin's advice when strictly necessary - the rest was your own wizardry!

(Special thanks to c1ash) There are eight times in the story when Alfred (or a note in the case of the first time) will suggest asking Merlin for advice, and usually Merlin will direct you to a new book.
However at least four of these Merlin sections can be skipped entirely.

1. (TALK) Gilgamesh: First visit after reading the note.
   
2. (TALK) Gargantua and Pantagruel: After arriving at the kitchen in Gilgamesh.
   
3. (TALK) Popol Vuh: After receiving the recipe from Pantagruel. Ask about tomatoes ONLY, the other options lead nowhere.
   
4. (SKIP) Sisyphus and Bellerophon: After finishing the recipe and the audience with the queen, you'll be in the stables. Instead of going to Merlin like Alfred suggests, open 'Sisyphus and Bellerophon (The Myth of)' in the library catalogue.
   
5. (TALK) Around the World in Eighty Days: After speaking to Bellerophon and you need to find a way to climb Mount Olympus.
   
6. (SKIP) Jack and the Beanstalk: After finishing the Around the World in Eighty Days section, just open 'Jack and the beanstalk (English fairy tale)' in the library catalogue.
   
7. (SKIP) Thor: After you are tasked with destroying the golden gate atop Mount Olympus, just read 'Thor (The Myth of)'.
   
8. (SKIP) The Divine Comedy: After finding Gilgamesh, just read 'Divine Comedy (The)'.

The achievement unlocks during the credits, when Merlin is show on screen.



Alfred Walsh - Chatty Man
You spoke to many, many characters about many, many things!

I don't know the exact requirements for this besides exhausting as many dialogue options with as many characters as you can. I unlocked this on the same playthrough as "Ker'aooc The Wizard", so you can safely skip asking Merlin for advice (except for the four times needed to progress the story).

Below is a quick list of all the people in the game.

KING ARTHUR
- Merlin

GILGAMESH
- Merchant
- Soldier
- Soldier (both soldiers say the same thing, but with different voice actors)

- Atab: exit the kitchen to talk to him
- Queen Ninsun (story)

- Utab
- Urshanabi, the boater

- Gilgamesh
- Oblivion

GARGANTUA AND PANTAGRUEL
- Drunkard

- Pantagruel
- Panurge
- Drinker
- Glutton
- Drinker (can't actually converse)
- Glutton (can't actually converse)
- Drinker (can't actually converse)
- Glutton (can't actually converse)

- Innkeeper
- Miller (story)

POPOL VUH
- Iktan

- Mayan Woman
- Tradeswoman

- Mayan guys (part of the story, but ask about tomatoes first)

- Papan

- Gambler (story)
- Papan (story, outside temple)

SISYPHUS AND BELLEROPHON
- Passerby
- Bellerophon

AROUND THE WORLD IN EIGHTY DAYS
- Passepartout, Mr. Fogg's Valet
- Phileas Fogg

JACK AND THE BEANSTALK
- Jack's Mother
- Jack

THOR
- Unknown Man (Loki)
- Unknown Man (Thor)
- Alberich

DIVINE COMEDY
- Dante
- Charon
- Enkidu

The achievement unlocks during the credits, after all the voice actors are credited.



Lord Of The Files
You played the game from start to end without autosave or saving!

Self-explanatory. Recommend you do this on a fresh playthrough without worrying about other achievements.
A speedrun of this game skipping all dialogue and cutscenes will only take around 45 minutes.

These 5 achievements can be missed because they require you to solve a puzzle in your first attempt.
As I mentioned in the first section, PROTOTYPE303 has written a guide with the puzzle solutions here: https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=1655421325

Riddle Me This
You solved the tavern riddle in one attempt!

On your first arrival to Gargantua and Pantagruel, you need a password to access the Tavern.


Burglar Bill
You opened both Panurge's box and the Giant's box on the first attempt!

Note there are two parts to this achievement.

• First box is inside the Tavern in Gargantua and Pantagruel
  
• Second box is much later in the game, in the Giant's House in Jack and the Beanstalk

Inspect A Gadget
Using superior engineering skills, you fixed the mill mechanism in one single swift swoop!

Also in Gargantua and Pantagruel, when you need to fix the mill to make flour.


The Man, The Myth
You solved the Mayan Creation Myth puzzle in 1 or 2 attempts!

In Popol Vuh after completing the kicking minigame and you are sent to the temple.


Classy Classicist!
You solved Athena's riddle in 1 or 2 attempts!

In Sisyphus and Bellerophon, at the top of Mount Olympus.

These cannot be missed and will come naturally by playing through the storyline.


Arthur and the Knights of the Round Table
You travelled into a book and met Merlin the wizard!


The Great Escape
You escaped the prison of Uruk, great!


The Password to Larkspur Lane
You solved the password riddle and gained entry to the inn!


Immortal Twin
You escaped from the Mayan temple!


Gargantua and Pantagruel
You completed the Gargantua and Pantagruel tale!


Around The World In 80 Days
You completed the Around The World In 80 Days tale!


Popol Vuh
You completed the Popol Vuh tale!


Jack and the Beanstalk
You completed the Jack and the Beanstalk tale!


Thor's Hammer
You found Thor's legendary hammer!


Sisyphus and Bellerophon
You completed the Sisyphus and Bellerophon tale!


Gilgamesh
You completed the Gilgamesh tale!


The Divine Comedy
You completed The Divine Comedy tale!


Tales
You defeated Oblivion and saved the Tales!

These two achievements don't fit in any other section.


Yellow Brick Road
You were curious about The Wizard of Oz tale!

At anytime during your playthrough, click the "Oz (The Wizard of)" entry in the library catalogue. Nothing actually happens, other than the achievement unlocking.


Artamène ou le Grand Cyrus
You completed every achievement!

Self explanatory. Assuming you followed my advice, this will unlock after you finish your no-save playthrough.