As you start playing, you get introduced to the basic mechanics of the game... but no one tells you how to use those mechanics to survive in this game.
My goal in this guide is to teach you how to play the game so you can survive it, even in the hardest difficulty.

Lets get started!

NOTE: Maybe in the future I will record some videos to show some stuff that I mention in this guide!

Humans are together with the Joes (Androids) the easiest enemies to deal with.
Why? Because they are weak against your weapons, they are easy to distract and they are kind of blind... lol
What you should be careful is that they have ranged weapons like Revolvers and Shotguns that deal several damage in the hardest difficultys and also they will atract the Major threat (the Alien) with their shots.

What to do against them?
Based on the situation you should decide when to be sneaky and when to be aggressive.

I use my stealth as much as I can, throwing some flares to distract humans (flaresdont make noise = no Alien) walking while CROUCHED A LOT (Seriously, this will make you almost invisible!)
Sometimes you will get spotted and yor best option will be to run while shoting and clearing your path to get to a safe spot where you can wait for the waters to calm down...

An awesome option is to "call" the Alien by hitting something with the Maintenance jack or a NoiseMaker and hide under something, behind something or inside a locker (a lot of people say that lockers are death traps but I found them usefull even in Nightmare. Note: Only the tall lockers, the small metal boxes ARE death traps. Use them on your own risk)

The Androids or Working Joes are all around the station so you will encounter them a lot.
There are 2 types of them:

The Normal Joes
They are though to kill with the soft weapons like the revolver or the Maintenance jack (you will need to backstab them a couple of times or stun them to do it)
You can use the fire but its not a good option since this is your only weapon against the Alien (you should save it as much as you can)
They will easily die with the shotgun or the bolt gun.
Also they are very slow even when trying to catch you.

The Suited Joes
They are like regular joes but they are invulnerable to stun (EMP mines and Stun Batton)
You will need fire power to aggressively deal with them

How to deal with the Joes?
They are more... observant than humans (they will see you more easy), but they usually stick to a routine (walking around or working in some computers)
With the Joes you should try to avoid agression IF they are friendly (white eyes) dont attack them neither show your gun.
If they are in the agressive state (red eyes) treat them like humans: hide, sneak, distract and if needed attack and kill them.
One thing you should be very carefull is that the Alien dont care about them, so if you are fighting with one or more Joes and the Alien shows up... well good luck then xD
They can grab you and soround you if theres many of them, so watch put for that too. Also be very carefull when you take them out with a stun+hitting wih melee because this can atract the Alien!
And the last tip is to watch out for the ones that are in the floor with the eyes opened... they will grab you and will kill you if you are low healthed.

This Bastards will insta kill you if they get to melee range so watch out for them!
They appear in the latest missions of the game (first time in the nest at the generator)
They are super easy to one shot even with the weakest weapons and they make a easy to hear scream before they run thowards you. Also they are inside closed eggs so dont get close to them, just burn them from a safe distance.

The one that probably bring you to the guide...
Fast, Lethal and INMORTAL!
First lets talk about his weakness FIRE. The flamethrower is the best option to avoid getting killed when he attacks. He falls back and then runs away or you burn him while he is attacking so you will recieve damage but he will run away (if you have low health he will kill you)
You can also use a molotov to make him run away or a pipe bomb.
NOTE: there's no need to use more than just a click to give him a burn and make him fall back, if he is still after you burn him a little bit more until he runs away.
NOTE 2: When you make him go away it will be just for a very short time, because he will know your position and he will come back for revenge. The only way to make him forget about you is to hide after he is gone so he will think that you are gone.

The best way to deal with the Alien its not making him run with you weapons, you have to use them only if he spots you. What you should do is to stay sneaky.
-Use tables boxes and chairs to circle arround them while being crouched. This is by far one of the best ways to pass right by his side without him noticing you! Also you can use this when he is coming and you are low or dont want to waste utility.
-Noisemakers are awesome when he is lurking in the corridors far from you and you need to go where he is.
-Flares are awesome when he is close to you because they will inmediatly atrack him and give you some space to move and sneak to take distance from him. (Flares wont atract him if he is far away because they dont make any noise).
-You can use a Smokebomb to pass through an are where he is standing
-As previously said: big lockers can be used if needed, they are not the best option but sometimes they are useful.
-Always watch out for the vents in the roofs... if you hear a "HISS.." and you see some slime falling be careful, he will insta kill you if you pass under him.

A final tip is to avoid being in very low health... there are some environmental events that are unavoidable that will hurt you and can insta kill you if you are too low on health.

Tired of the intros? Don't know how to skip them?

Easy fix:

1 G to: "C:\Program Files (x86)\Steam\SteamApps\common\Alien Isolation\DATA\UI\MOVIES"
2- Rename this files: "AMD_INDENT.USM", "CA_INDENT.USM", and "FOX_INDENT.USM"
Add a _ or anything to the name of this files and you are done.

Hope you learned something on this guide or find it useful!

My natal language is not english so I might have grammar/orthography mistakes xD
Feel free to comment, critique, ask, suggest... etc.

In case you want to check it out here is a full gameplay of me in the nightmare difficulty
https://www.youtube.com/playlist?list=PLQYKAGUKLEmwVuOLRP20OgFT8oarYtX7D

:)