One thing that will really help... shoot some skeet (or trap, but skeet is better training IMO).
I recently shot my home defense 12 gage after an afternoon of shooting 22 rifle at bullseye targets. Without thinking too much, I shouldered the mossberg in a fully bladed offhand rifle position, pulled in in lightly into my shoulder pocket, squeezed the trigger.... and then realized that the recoil seemed a lot more severe than the last time I shot it...
Of course I was using the exact wrong position for shooting a shotgun. Once I squared up, leaned forward, and pulled the gun in TIGHT to my shoulder, I went through the rest of the box of shells without problem.
The point is, we revert to our training, and I had been training all afternoon with a 22 rifle.
Shooting skeet will get you used to swinging the gun at a moving target, absorbing the recoil, and following up with a second shot.
You don't have to be a great skeet shooter... In a self defense situation, a human enemy is much larger, and moving much slower than a clay bird.