Alien: Isolation

Complete the game without killing humans.

This solution will tell you where humans will be encountered and how to avoid them. As far as I know there is no non lethal method of taking down a human. (If anyone has knowledge to the contrary please let me know). It's implied in another achievement description that there is but I missed this on my first play through after trying to knock someone out with the maintenance jack, and trying to stun with the stun prod. These also added to the achievement counter for killing 10 humans which is why I would advise you to just avoid the humans or when difficult use an alien to do your dirty work for you!

Mission 3: Once you get to the lobby you will see a woman standing in front of the elevator. Run towards her and duck behind the reception desks. She will fire twice and then run off to get her friends. As soon as she has finished firing you can proceed to the objective and grab the security access tuner. Then start running up the left stairs which will be on the opposite side of the lobby that her group will be coming from. Keep running south on the far side of the couches and stop when you get to the small set of stairs. Now just walk through the room with the 2 elevators and out the other side to the west. On your left will be a guy facing the other way. Just keep walking towards the objective marker and you will be fine. When you return here wait for your new friend to finish eating then carefully walk to the elevator to Seegson Communications.

Mission 6: While on the primary care floor you will find a few humans in the hallways. If you go to the entrance after obtaining the trauma kit there will be one walking a way from you which you can avoid by cutting through a room on your right. But you can skip all this by going straight to the Power Plant and Samuels will radio and update your objective to initiate the evacuation procedure. On your leisurely walk back to the entrance cut back through the operating theatre (where you got the trauma kit) to avoid the humans, the Alien usually will help you out by thinning the crowd and keeping them occupied.

Mission 7: When you need to "Find a compression cylinder to repair the elevator" there is a clear path to avoid the humans starting with a vent on your right. As long as you don't stray from the path you can just keep moving until up the ladder and then you are pretty safe. After completing the objective, you won't need to worry about those humies anymore.
Now once you get to the Synthetic Fluid Plant there will be 2 humans on the far overhead area looking down on you. Smoke bombs will do nicely here while you do some rewiring. Once done the humans will either stay up the top (take the activated door on the left) or they will come down and out the door you opened leaving you free to go up the ladder and on your way.

Mission 8: You will be sent to fix the transit system. After activating the 3 green screens a human will walk out. Hide nearby and wait for him to do his usual routine of walking clockwise around the set of consoles you activated earlier. While he does this you can go activate the lever that is to the right and behind when facing the middle 3 green screens. Once you do this you need to activate more green screens on the left and to the front. Just be careful as the human may decide to go the opposite way but mostly he just goes around the room. Now hide while the human is taken care of and replaced by an Android with pretty much the same predictable path. You can kill him if you like. After activating the middle consoles again you can go. If you know exactly where all the consoles are and the order you need to hit them in just walk straight to them all without stopping and the human shouldn't see you, you will be back at the last middle console as the android is butchering that human you're not allowed to kill!
Once you get back from fixing the transit system Waits will let you know they heard voices as they were leaving. Push the button to call your objective transit and then hide in a locker opposite the transit. Just wait a while and the humans will come down and talk and then eventually leave so you can get in the transit car.

Mission 10: The only humans in this level are not hostile so don't try and hide from them for 5 minutes until you get close enough to realise Ripley talks to and warns them about the Alien. I never did that, not me. Nope.

Edit: Jan 2017. So Tuxie in the comments had this to say: "About mission 10. After returning to the elevators from locking down the corridors at the server farm, I ran into people on the upper level. They immediately opened fire and I had to throw a noise maker there to get rid of them. So not everyone on mission 10 are friendly." I was a little surprised to hear this over 2 years after but I can't check and I don't remember so use the above comment with caution and please confirm it for me if it's true! Thank you Tuxie for your comment!

Mission 16: These humans are probably the most lethal in the game so It would be nice to kill them but they can be avoided without too much trouble. From the door you need the Ion torch to open walk forward to the steps and then crouch, keep moving forward while hugging the left wall. There will be a shotgun guy in front of you, wait for him to turn around and then use the ion torch to open the vent on your left. Get in and follow it to its end, then turn left and walk forward to another vent on your left. Once out the end of this one, turn left down the stairs, turn right into the room and move the end waiting on the left side of the door crouched in the corner. Peek around the corner, there is a shotgun dude in the middle of the room. If he is walking towards you go back to the corner and wait for him to come down almost right next to you, then walk past him into the next room. If he is walking away you can go straight away. Stay on the left side of the room so you are covered by all the consoles in the middle. Once you get to the end check on your right that the guy isn't there and then proceed down the stairs into the small room and take the vent. Go up the ladder, open the hatch and then be careful as another shotgun dude is patrolling this last hallway. If he is right there wait for to turn around then follow behind him until he goes into the room where you originally got the motion tracker. Cut across the hallway and proceed upstairs.
Once you are upstairs, said hi to Ricardo and gone up the elevator you will encounter your last few humans. Exit the elevator and turn left at the end of the hallway, staying behind the table and chairs. Open the vent and drop down then just keep going straight forward where there will be a little door that you can exit the vent. Just keep moving turning left out of the vent and towards your objective.

Mission 18: Towards the start of this mission there will be one part where you are in a small area with a couple of shotgun guys and you have to power up some stuff. You can sneak around them by hiding behind the boxes but I think it's more fun to throw out a noise maker and let the Alien do what it does best.

I realise I may have been a little vague at times I just didn't want to spoil anything. You should know what I'm talking about once you get up to each point I'm talking about. Hope this has helped and please contact me if you need any advice with this game.

If you accidentally kill someone, reload your save immediately and it should still pop at the end.

I accidentally used a flame thrower on a lady but reloaded my save and it still popped at the end, and I even got credit for the kill 10 humans achievement.

Here's a guide I put together to help with this achievement, I played through on Nightmare although i'd recommend going through on an easier difficulty, the strategies in the video will work just the same. Hopefully the guide helps some of you out.