This picture perfectly illustrates the correct way to stand in a tactical, ready to go position. This position makes it easy to move into a crouching position.
Step 2: Bro, do you even crouch?
Crouching can vary depending on the position of your target. You may get lower, or you may raise up to get that kill. This is the basic way to crouch.
Step 3: Lay it down
Going prone can be a vital decison while being hosed by an enemy. When in the crouch position, you move your trigger free hand to the ground and throw your legs back. The leg directly below your hand which is on the trigger should be hiked up (like you're humping the ground). It may feel weird but will help in transfering through positions.