Here's some useful things I picked up during several plathroughs.

Character build

It's acctually pretty hard to REALLY mess things up in this game even if you don't have the stats to succeed the checks. The story will go on regardless. But if you want to have the best outcomes it's best to pick a focus and stick to it. Pick a few skills to max out rather than having a few dots in everything.

Skills and Attributes go together so it's easier to pick a focus based on that.

My most common builds:
Combat focused: DEX/STR + Combat, Athletics
Talk focused: CHA/MAN + Persuasion, Subterfuge, Leadership
Supernatural focused: RES/COM + Occult, Faith

Honorable mention to DEX + Clandestine combination that pops up a lot if you wanna snoop around.

Occult vs Science & Technology

If you have to pick between the two, I found Occult has more uses.

Faith

Faith is a very useful Skill to have high and you can only start investing in in once you're past character creation. If you don't know where to put experience points it's usually a safe bet.
Having high faith is important to getting several acheivements.

Willpower

Willpower is calculated by adding your Composure and Resolve. Over the course of the game you have opppotunities to lose it and gain it back up. To trigger some events and acheivements you need to have at least 7 points of it.

Backgrounds

Out of the three background oprions I found having maxed out Resources is the most beneficial. It allows you to afford whatever weapons you like as well as buy your way out of several situations down the line, biggest one being saving Grandpa's store.

It's pretty easy to start the game with maxed resources (see character building guide for more details).

I wouldn't put many points (or any really) in Influence as it's something you can gain with the actions you take during the course of the game.

Super Human
Raise an attribute to five dots.


Easiest way to do this is to pick the highiest Attribute from character creation (should be 3-4 dots)
and save all your EXP to raise it to the maximum.

Skill Master
Raise a skill to five dots.


This one is easiest acheived during character creation.
When choosing what you studied pick "I customized my education… [Advanced players.]" and simply put 5 dots in the skill of your choice.

Allying with the Young Vampires
You have allied yourself with Monroe Duncan and the young vampires. (Secret)


This one is easy to get, when Monroe approaches you during search for Tyler, simply agree to help out her group.


Blood Kiss
You let a vampire feed on you during sex. (Secret)


There are two ways to get this one.

Easiest is to agree to help Amanda, when she offers you romantic advances, go along with it and you'll get the acheivement.

Alternatively if you don't help Amanda and have a good relationship with Monroe you can get the acheivement from her instead.


Gift of Blood
You have been given a gift of a vial of the blood of the vampire. (Secret)


When dealing with Monroe's group say you want something in return in exchange for your help and ask to be turned into a vampire. They will explain they are unable to turn you and you'll get the vial instead.


I Put a Spell on You
Place a curse on a mortal or a vampire.


If you have decently leveled up Occult skill (I recommend at least 4 dots) you'll get several opportunities to place a curse on someone at the cost of your own Willpower. (ex: during Duke's rampage or during Perry's attack)


Romance in the air
End the game with a romantic partner.


Fairly straightforward someone for a date and stick to the realtionship. Most obvious choices are people in your hunting group but Monroe is an option as well. Adam is the easiest to get since he asks you out on his own, but anyone will do.


Saved by a Vampire
A vampire saved your life. (Secret)


During Perry's attack either call for help and choose a vampire to come to your rescue or fail to defend by yourself and Amanda will come deal with him, gaining the acheivement.


Sensed Undead
You sensed a new acquaintance was really a vampire. (Secret)


Have a Faith of 4+ dots by the time you meet Jace at the doctor's office and the acheivement will trigger. Also possible to get when meeting Mikayla's friends before final confrontation.


Unbreakable Will
Resist a supernatural power.


Have a Faith of 4+ dots and it'll trigger during several endings. Ending 1 for sure as well as several others.


Vampire Hunter
Destroy a vampire.


During Perry's attack have high combat skills, buy some decent weapons at Marcus's store beforehand and have your store reinforced. Defeat him without help and you'll get the acheivement.
Destroying either Amanda or Monroe later in the story does not count towards this one.


Hidden Room
You found the hidden room in your grandfather's house.


I honestly never figured out for certain what stats affect it. Probably decent Awareness? I do get it on most playthroughs so it can't be too high.


Stop the Rampage
You stopped Duke Bowie without a loss of his life.(Secret)


You need to convince him to step down (need high CHA + Persuasion) or shoot him yourself (need high DEX + Combat).


Store Saved!
Save your grandfather's store from foreclosure.


Easiest way is to have high Resources (at least 4 dots to pay the loan in full) and tell the Mayor you want to pay if off before the final confrontation with Amanda.

Alternatively you can ask Amanda's help with that as one of the conditions for helping her deal with young vampires.

Below are lised the conditions you need to meet throughout the story to reach a specific ending.


Ending 1 - Hello from Chicago
Damien cleans up Jericho Heights. (Secret)


Don't agree to help Amanda or the young vampires. Have a high Path of Righteousness. Meet Damien before the final battle by following Mikayla. Have Amanda survive the final battle. Expose masquarade breaches whenever you can by telling people about vampires.


Ending 2 - Where the Hell is Horseshoe Bend?
Placed in witness protection by the FBI Special Affairs Department. (Secret)


Have a good relationship with Amanda. Make Amanda and Monroe reach an understanding during the final battle. Expose masquarade breaches whenever you can by telling people about vampires.


Ending 3 - Embrace the Darkness
Experienced unlife as a vampire. (Secret)


Have a good relationship with Amanda and agree to help her. Make Amanda and Monroe reach an understanding during the final battle and have a high Path of Immortality. Don't try to expose masquarade breaches by telling people about vampires.

Alternatively Ask to be turned into a vampire in exchange for helping Amanda then follow through.


Clan Thin-blood
Became a vampire of Clan Thin-blood. (Secret)


Have less than 7 dots in Willpower when embraced by Amanda.


Clan Toreador
Became a vampire of Clan Toreador. (Secret)


Have 7+ dots in Willpower when embraced by Amanda.


Ending 4 - A New Take of Mortality
Became a ghoul of a powerful vampire. (Secret)


Have a good relationship with Amanda and agree to help her. Make Amanda and Monroe reach an understanding during the final battle. Don't try to expose masquarade breaches by telling people about vampires.

Helps if you ask to become Amanda's servant in exchange for your help.


Ending 5 - The Power of Tourism?
You have agreed to join Amanda Chastain's initiative of bringing new mortals to Jericho Heights. (Secret)


Have a good relationship with Amanda and agree to help her. Kill Monroe during the final battle. Don't try to expose masquarade breaches by telling people about vampires.


Ending 6 - The Eternal Enemy
You have made a powerful enemy in Amanda Chastain. (Secret)


Have a very bad relationship with Amanda and refuse to help her. Have Amanda survive the final battle. Don't try to expose masquarade breaches by telling people about vampires.

This ending was the hardest to get for me. You need to keep your Paths low for this one or you'll be thrown into a diffrent ending instead. Also be careful to keep Amanda's relationship low as it's a lot harder to lower it than to raise it (one misclick can undo all your progress)


Ending 7 - Gone for Good
Monroe fails to reconcile with her Sire and leaves town for good. (Secret)


Make Amanda and Monroe reach an understanding during the final battle. Have a very good relationship with Monroe. Don't try to expose masquarade breaches by telling people about vampires.


Ending 8 - More Human
In killing her Sire, Monroe has escaped the curse. (Secret)


Kill Amanda. Have a very good relationship with Monroe. Don't try to expose masquarade breaches by telling people about vampires.


Ending 9 - A Hunter's Life
You have teamed with Annis Kean to hunt vampires across the USA. (Secret)


Meet Annis Kean by mentioning vampires to Zane or calling the police during Perry attack. Kill Amanda with Annis surviving the final battle. Don't try to expose masquarade breaches by telling people about vampires.


Ending 10 - The Arcanum
Joined the secret society, the Arcanum to study the supernatural. (Secret)


Have a high Path of Knowledge. Doesn't matter how you dealt with Amanda. Don't try to expose masquarade breaches by telling people about vampires.

I recommend keeping Path of Knowledge low unless you're going for this specific ending, as it tends to trigger instead of some of the harder to get ones.


Ending 11 - Becoming SAD
Became a consultant for the FBI's Special Affairs Department. (Secret)


Have a high Path of Righteousness. Kill Amanda. Don't try to expose masquarade breaches by telling people about vampires.


Ending 12 - Filling the Void
With Amanda Chastain gone, a new owner moves in to Bleakrest House. (Secret)


Kill Amanda (I did this while being antagonistic to her, not sure if offering to help her then changing your mind affects this). Don't have a high relationship with Monroe. Don't try to expose masquarade breaches by telling people about vampires.

Try keeping all the paths low for this one or you might trigger a different ending.