Our procedure was very simple, and we were trained to not deviate from it.
1.
Never give up control of your weapon until the cavalry arrives. In our jurisdiction that meant holster or hold, depending on the circumstances. Never place your gun on the ground until the good guys arrive.
I do not want to be in the open with a visible firearm when they arrive. I want to see them before they see me
Really bad thinking
2.
Make yourself obvious to the cavalry. If holding on a bad guy, you want to make damn sure the cops don't find you by surprise, or worse yet, have to go looking for you. If you can arrange it so that you are
the first and most obvious thing they see when they pull up, do it.
3. Once the cavalry arrives, raise both hands in the air. Turn toward them, show them the gun, place it on the ground in front of you, in plain site of the officer, and step back at least two paces. Place both hands on your head. If you can safely do this before being told to do so, so much the better.
The reason for this should be obvious. You want them to know they have entered a situation involving a firearm, and you want them to know where yours (at least) is.
4.
Follow their instructions. Expect to be cuffed. Cooperate when they do it.
5. Every body will be running on adrenaline,
don't add to the problem.
6. Finally, and most important IMHO,
keep your mouth shut! When asked a question, give a short and direct answer. Most street cops aren't looking for your life history, and they're going to turn you over to a detective any way. The less chatter and noise they have to deal with, the better as far as they are concerned. If you are a civilian, it is usually best to ask for an attorney, even if you feel you did nothing wrong. Again, the reason for this should be obvious.