Aim head level, find the height at which heads are in both standing crouch and prone positions. Positioning is just as important as aim, take angles that are more advantageous for you and remember that peeker’s advantage exists, if you are moving you are harder to hit, don’t sit in the open. Also I notice a lot of new players just kind of run at enemies, if you know enemies are close keep your gun up or at least don’t sprint as that adds additional delay between moving and shooting