Good for health in general but not on Sevastopol station.First and most important tip is don't sprint at all.Sprinting can alert the alien and other threats near.Sprinting can also trigger some glitches like "the never go in vents alien".

The vents and closets are not the best choice to hide.Leave them as your last resort,especially the small closets.I have tried to make a statistic of death/unseen on small closets and I got to the conclussion that they are almost useless.Also closets would be ok if they would not make the terrible sound when entering them(the door slamming).I for one preffer tables as they can offer a possibily to craft items,move a bit and more visibility.A good spot would be in the dark when playing on low difficulties as the ai is idiotic enough to not observe you(don't recomend on hard->nigtmare).Vents with drolls coming out mean alien is camping there so don't get curious .Seriously Sega,what kind of normal people who would want to live slam doors at a stealth game?

Finding the blueprints is vital.I recomend crafting as much as you can,as they can get you out of an improvissing situation that is going bad.Best items in my opinion are:medical kits(of course you need them),molotovs(if you aim right they can save you from that nasty situation),emps(ONLY for simple androids,they don't affect the hazard suited ones),and noisemakers to lure hostiles to certain locations.So guys Ripley is engineer class 2,give her some things to craft!

Nice guy,if you are like the predator or something.Otherwise,as a human mortal,best to avoid him.Here are some usefull things i can share with you:
1.Don't try to run if you see him,hide better always.
2.You can't kill him,this is not Call of duty or Battlefield so don't go Rambo on him.
3.If you are standing up and walking,his vent spawns will be more often as you make a bit more noise.But from what i heard the noise difference is not so high so you decide which tactic you take,regarding the stand-up-walk or crouch walk.
4.If you don't have a place to hide,as a last resort,stay still in the dark as he is a dumb animal in some cases and won't see you.Avoid fire explossions or lights as you are a sure target
5.If you fail to complete any of the advices,my last advice is collect fuel for flamethrower as much as you can or pray more.

The guys who invented a mobile phone operating system.Ok,they didn't but they are still are a big deal in this game.Dealing them is easy if you have the certain knowledge.Simple androids can be killed in these matters:
A.with either emp+tap melee E(my personal favorite),it's good for stunning multiple androids at the same time
B.stun batton+tap melee E
C.2 shotgun shells in their face
D.3 bullets(novice->easy difficulty) or 4 bullets(medium->nightmare difficulty)-carefull on hitting the head not the shoulder by the way
The hazard suited androids are more difficult to deal with so i recomend next ways:
A.Using pipe bombs(and be carefull on not throwing too close to yourself as it will result in your immediate death,and try to craft them at maximum-see mission 13-consulation where there are androids that are gathered in pairs,right and left in the first part then 2 more at the final part)
B.2 shotgun shells in their face(not available for mission 13 where android paradise breaks loose)

Ok,next thing is humans.Don't aim guns foolishly at them as they can take it as a threat.Try going stealth in my opinion.Remember mr.alien has very good hearing sense and can hear if you are being naughty.In some missions they get hostile on sight in some they can let you retreat.Stay still is considered an act of agression,same as aiming a gun at them.If you shoot a human quickly run to hide and grab something to eat.This will take a while as the alien ai gets suspicious.And by the way,the security guys who are armed to teeth only drop 1-2 bullets...

6.Facehuggers-in my opinion they are the biggest threat in the game as they move fast and have fast death cutscenes so they make things difficult for one shot trophy.I for one learned their locations aproximatelly and use shotgun on them cyka.BUT I strongly recomend using flamethrower in bursts if you are not sure.I reffer to mission 18-Tomorrow,together.Try to locate CLOSED eggs as they are the only ones who can produce a facehugger.Also on the mission 15-The Anesidora watch out for a facehugger(in the room large room with a terminal log,as you go for Marlow objective.after you turn power back on) and mission 17-desolation where you have a hugger located in the transit control room.The most important facehugger location is the central core reactor maintenance,where you will have about 5-6 facehuggers(don't know the exact number now),go slowly there and always have flamethrower prepared but don't light it up as it can attract the aliens from beta core(right click mouse).