Things I learned the hard way and some odds and ends:
Use low-brass 2 3/4" shells to start, not hi-brass. They kick less.
Get your elbow up, out, and hortizontal, and then put the butt of the gun in pocket formed by your shoulder and your chest.
Hold the gun firmly against your shoulder. Very tightly, with full contact if possible.
Get one foot out in front and lean forward into the gun and the shot. Don't stand flat-footed and shoot while you're all loose-jointed and relaxed. Shoot with purpose.
Don't lean back and shoot with your shoulder up against a tree or a post. You'll be sorry.
Keep the thumb on your trigger hand away from your nose. Let your shoulder deal with the recoil.
Keep both eyes open. Concentrate on the target. Can you raise your hand and point your finger without sighting down it? Look at the target and point the shotgun. If the target is moving swing ahead of it. OTOH, if it has rifle sights you have to shoot it like a rifle.
Take a lesson from someone who knows what they're talking about.
Don't load the gun until you figure out how it works.
Don't point it at me.
When stuck in duck blind with someone you don't know, stand very close to them. It makes it harder for them to point the thing at you when you're not looking.
That's all I can think of right now. Have fun.
John