When you are throwing a can or a bottle, hold L to throw it harder and further.
Save ammunition
If you find a room being patrolled by a guard or worker, wait until he leaves, then turn off the light switch. When he returns, he will immediately move to the light switch to turn it on. At this point, his back should be turned to you. Quietly sneak up and either grab or punch him without firing your weapon.
Faster manual lockpick
When using the manual lockpick, instead of rotating it slowly as the game suggests, press the Analog-stick in one of the four diagonal corners, as the "rumble" will always be in one of those directions. This is much quicker.
Avoiding detection
Always try to stay in shadows or bushes; crouch when walking around; try to take someone hostage before shooting them; always try to use your night vision/thermo goggles just to check to see if there is anything to get around you; and drag bodies into dark corners.
