You can use any of three stances during your mission: standing, crouching, or lying on the ground (prone). Standing is only good for peeking over obstacles if you need to survey an area, and even then, you should only pop up for a second so that you don’t get spotted.
Crouching will be your main stance; it’s your default position for moving slowly, but steadily, and being able to line up a standard shot at a moment’s notice. Dropping prone affords you great cover—you’re low to the ground, after all—and steadies your aim, especially for long-range shots, but it limits your movement to a crawl.
Enemy position dictates how you should move. Most of the time you don’t have to move; you should stay still in cover and pick off all targets until the coast is clear. When you do need to move, make sure you know where all the surrounding enemies are located before you take off.
If you want to cross an open space like a field, for example, and there are no enemies in sight, stand up and sprint to the other side before others arrive. If you’re in average terrain with lots of cover spots like rocks and trees, crouching tends to attract the least attention.
In heavily guarded areas where you have to stay put or where you have to move only a short distance, crawling in the prone position may be the best option.
