1. Your task will never be to eliminate all your opponents. However, if you decide to kill a couple of enemies, you should be careful - gun shots can be heard from afar, and after two shots opponents will be able to establish your position. It's best to change positions after every shot you take.
2. Your opponents are smart - they often change their positions, can aim well (even on the lowest difficulty level) and can use the surrounding objects. That is why you should not take cover behind e.g. vehicles that can explode.
3. In certain situations you can use noise to your advantage (e.g. incoming planes, thunder etc.). During such moments, a white icon will appear in upper part of the screen. You can assassinate opponents with a loud weapon without worrying that that opponents can track your location. However, if a soldier finds a fallen body, he will investigate that (not knowing where the bullet came from).
4. Don't be afraid to raise the alarm. If the enemies don't know where you are or they are feed up with looking for you, they will become careless again. Furthermore. Not all of them will be informed about your presence, so you can move to the next area and soldiers will not be looking for you.
5. You will get points for each kill. You get additional points for headshots and performing additional activities, such as killing two enemies with a single bullet, throwing objects at them, killing them in an explosion or performing silent assassinations. Use points to advance to a higher rank, and thus unlock additional equipment that you select at the beginning of a mission. You will get additional points for destroying hostile vehicles.