Conserve your ammo, always sneak attack (stab a target before they spot you) when you get the opportunity, it has the added benefit of providing water.

Conserve your water, do not heal up (backspace) when you are only at 10% damage, you will still use as much as 25% of your water to heal. Wait until you are at 25% damage or worse, otherwise you will run out of water quickly.

Do not use peeking around corners to check out whether or not a guard is in the next room or hall, you will be spotted if the guard is looking in your direction. Instead, move Paul close to the corner (without touching it or exposing yourself) and move the camera angle (using the mouse) until you get a clear view of the hall or room. This will allow you to plan your attacks.

Continue to use peeking around corners if you must get in a gunfight since the wall will provide cover for Paul.

When you run out of ammo and you cannot sneak attack a guard, run up to the guard and allow him to hit you until you are below 20% hit points (the health bar will turn red). Left click rapidly while under fire and eventually Paul will use the voice to paralyze the guard. Left click with the knife again to neutralize the target and take his water. This is the only way to finish a mission when you have used up all your ammo, and it is only available once Paul has been tested by Alia, after his mission to destroy the harvester.

The best way to move Paul around is by changing your perspective with the mouse and pressing the up arrow key to make him walk in the direction you are looking.

There is no way to skip cut scenes.