The moment after you use your firearm for self defense, you must contact the authorities as soon as possible, if they haven’t arrived already.
When they do arrive, place your hands where they can be clearly seen. Lay your firearm down on the ground. Engage the safety on your firearm beforehand if it has a manual safety.
Always obey what the police officers tell you to do. Even if you feel you were justified in the shooting and are innocent, the cops don’t know that (yet). As a result, they will be shouting orders loudly, act aggressive, and treat you as if you are a criminal. Remember, the cops are risking their lives by being on the scene.