Instructions
Find a location that's ideal for the prone position. Because you cannot move quickly when in the prone position, your location must cover you from the eyes of others, such as in a building or tall grass.
Press and hold the "O" button on your controller and you will drop to the prone position. If you only press the "O" button, you will drop to the crouching position.
Move the left analog stick up and hold "O" to dive into the prone position while sprinting. Your character will dive onto his stomach.