It is not possible to get all achievements in one run, so be prepared to spend quite a bit of time getting these.
Also, obviously this guide is NOT spoiler-free so consider only reading it if you are really stuck on getting an achievement. I try to keep them as spoiler-free as possible...which isn't much.

The achievements are roughly in chronological order based on the story. If a specific trait is needed or will stop you from getting it, I will mention it as well.

I might update it further for future episodes, but so far this (obviously) only covers Episode 1 and 2.

Linguini Ratatouille
End Episode 1 with the trait Talk to Animals


The Very Hungry Caterpillar
End Episode 1 with the trait Book Smart


Bell Pepper
End Episode 1 with the trait Hot


Ebony Dark'ness Dementia Raven Way
End Episode 1 with the trait Mystical


Steve from Blue's Clues
End Episode 1 with the trait Keen Eye


Mx North Carolina
End Episode 1 with the trait Powerful Build


Candy From a Baby
End Episode 1 with the trait Street Smart


Junior Mouseketeer
When riding the car with Tabetha, welcome her to the Dead Mom Club.
When in the woods with Stella, after the conversation of your living situation, ask her about her own situation. Depending on your traits, you will have to dig a bit to have Stella mention that her parents are dead. Then welcome her to the Dead Mom Club.

That Damned Smile
Make Tabetha smile. There are multiple ways to make her do it, but the easiest way is to tell her you love PJ Sandwiches during the kitchen tour.

The Boy Who Cried Nice House
During the house tour, always pick the Lie option. Tabetha will call you out in the bedroom and you get the achievement. You can NOT have the Street Smart trait for this (as it makes your lies believable).

Cooking by the book
After the house tour, go to the kitchen. Go to the cupboard and get a knife and plate. Go to the pantry and get bread, then peanut butter. Go to the fridge to get jelly. You then automatically make a PJ Sandwich and get the achievement.

What were you expecting?
During the tour, pet the cat when you're leaving the kitchen. After the tour, go to the kitchen and pet the cat again. You can NOT have the Talk to Animals trait (as you will instead talk to her).

Urban Explorer
After the house tour, explore all three house areas (your room, the kitchen and the forbidden wing).

Hygge
While in your room, open the drawer to see an oppossum. Put your clothes into the drawer without chasing the oppossum out. The Talk to Animals trait doesn't matter for this.
NOTE: Thanks to boopsnoot for confirming that this achievement can be unlocked in Episode 1, not just in Episode 2 :D

Patient Zero
After the house tour, go to the kitchen and open the fridge. Open the take out and eat it. Swallow it, then go to town. Suppress throwing up on the way. While meeting Stella, suppress throwing up. You will then get the achievement in the diner. You can NOT have the Powerful Build trait (it keeps you from becoming sick).

Can You Pet the Dog?
Upon reaching the town, a dog will run up to you. The first choice upon seeing the dog allows you to pet it, use it. You can NOT have the Talk to Animals trait (it will have you greet the dog instead).

Old Yeller
When Duke is demanding of you to pick up the flashlight, do as he says. You can NOT have the Powerful Built trait.

Poor Trigger Discipline
When Duke is demanding of you to pick up the flashlight, pick up Gretchen instead. You can NOT have the Powerful Built trait.

Porqué no los Dos?
Have the Poweful Built trait. When Duke is demanding of you to pick up the flashlight, pick up Gretchen AND the flashlight.

Slumber Party!
After leaving the forest (and having met Sybil), accept Stella's offer to stay over at her place.

Good Cousin
After leaving the forest (before or after having met Sybil), decide to go back to Tabitha.

Jane Goodall
End Episode 2 with the trait Talk to Animals


Magic Treehouse
End Episode 2 with the trait Book Smart


Poblano
End Episode 2 with the trait Hot


Inspector Clouseau
End Episode 2 with the trait Keen Eyes


Anakin Skywalker
End Episode 2 with the trait Mystical


Mx America
End Episode 2 with the trait Powerful Build


Stealing Your Grandma's Credit Card
End Episode 2 with the trait Street Smart


Gretchen Sends Her Regards
Have the Talk to Animals trait and tell her during your first meeting that you have met Frou-Frou. Save Gretchen in Episode 1. At the start of Episode 2, while in the kitchen, talk to Frou-Frou and inform the cat that Gretchen is still alive.

Evil Has Triumphed
Have the Talk to Animals trait and tell her during your first meeting that you have met Frou-Frou. Don't save Gretchen in Episode 1. At the start of Episode 2, while in the kitchen, talk to Frou-Frou and inform the cat that Gretchen has died.

I Didn't Come Here to Make Friends
In Episode 1, agree to go with Stella to meet her friend after the forest (aka meet Sybil). In Episode 2, when you go to town, you meet Sybil and Avery. Wait until Avery leaves and she will want to leave. At the bottom of all the options, pick "What is wrong with you people?" and then click on all options to vent about every single character you met.

Alright Then, Keep Your Secrets
When you go to town, you meet Sybil and Avery. When Avery asks what happened, lie and say nothing happened.
EDIT: According to HexxedBoy, saying that you don't want to talk about it due to trauma also counts for this achievement!

Coffee Date
After Sybil and Avery have left, go to the diner and talk with Avery.


Just Browsing
After Sybil and Avery have left, go to the General Store. You can talk with the kid or not, but leave without taking anything.

Sticky Fingers
After Sybil and Avery have left, go to the General Store. Ask for potato chips, then take the potato chips.

I (Don't) Want to Believe
Have the Keen Eyes trait. In Episode 1, save Gretchen, then follow the creatures to find their nest. In Episode 2, while in the library, read the book about cryptids, specifically the first story. In the conversation after, mention the book, then that cryptoid and then say it was a mountain lion. When Stella doubts you, say there was a mountain lion in the creature's nest.

Just the Two of Us
In Episode 1, when Stella wants to go see her friend (Sybil) after the forest, decline and go home instead to meet Wayne alone instead of with Stella. After that, no matter in which conversation, don't mention him to anyone. In Episode 2, when you leave the library, the achievement will then unlock.
NOTE: I am not sure if it is needed since I happened to do it in that run, but to be really sure: In Episode 2, after waking up, look out of the window. Then, when in the kitchen, go into the garden and look for clues. Don't send the image or mention anything about what you found either.

Mystery Machine
After having visited Reese's house, agree to ride with Kaneeka.


Into the Woods... Again
After having visited Reese's house, agree to walk with Stella.


Nosy Nancy
While at the mine, talk to all three groups of miners at least once.


I Want to Talk to Your Manager
While at the mine, go to Tabitha's office. You have to do so before talking to the third miner group!

Stealth Run
Talk to max. two of the miner groups, then go back to Kaneeka and Stella.


Ronnie the Rat
Snitch on three different people. There are probably more ways to do this, but mine were these:

• Go to the General Store, ask about the potato chips, then go to the library and tell Kaneeka about having been invited to steal.
  
• When at Reese's house, tell the mom that you want to go on an adventure with him.
  
• While at the mine, go to Tabitha's office and tell her that Kaneeka and Stella sent you to snoop.

Out Of The Loop
When following the teenager, go into the mine without calling Tabitha.


Courtesy Call
When following the teenager, call Tabitha, tell her about what you're doing, but don't wait on her.

Minion
When following the teenager, call Tabitha, tell her about what you're doing, then wait on her.


Cutting Your Losses
Inside the mine, follow the children, then when you find Rosalina, grab her and leave.


No Man Left Behind
Inside the mine, follow the children, then when you find Rosalina, search for the other children.

Pro Babysitter
You need the Keen Senses trait. Inside the mine, during the argument between Tabitha and Stella, you will notice Rosalina is about to sneak out. Stop her/alarm the others to keep her from leaving. You will then automatically find the other children later and save them.