1. Apart from the default position, you can crouch or crawl. This will help you to take cover, move around without making too much noise and improve your aim. The disadvantage is that your speed will drastically decrease Running in crouching position is more effective (you make less noise) than scampering in your normal position. If you are close to your enemy, you can run up to him and perform a rapid melee attack. As long as he does not scream / shoot / use a whistle, the fact that you were noticed will not prevent you from performing a perfect silent kill.
2. You can use any objects to hide from your opponents: rocks, trees, walls, or even the very terrain when crawling. You may also hide in the bushes - you will remain safe until your opponent gets suspicious and decides search them (which doesn't happen too often).
3. The fact that you were spotted by the enemy, does not say a lot: when that happens, a yellow arrow that symbolizes suspicion will appear on the screen. Until it turns red, you can always hide, and if the enemy comes any closer, you can change your position or prepare a trap.
4. Hiding bodies is key to success. You can throw them at long distance, so this happens fast. It's best to hide them in bushes, buildings or throw them off cliffs. If enemies come across fallen bodies, they will investigate them and search the surrounding area. It's also a perfect moment to use S-Mines. You can attached them to a fallen body, and thus make them explode when the body is examined. However, things may get ugly if there are more enemies near the body, and not all of them will die.
Rocks and the whistle
5. You have unlimited supply of rocks. Use them often, as they will distract your enemies, and thus allow you to avoid them or sneak up to them and perform a silent kill (when running in crouching position, you will alarm the enemy when you are about 5m away from him).
6. You can also use your whistle. It will lure enemies towards your position (use this to set up traps).