My boss was the same way, late 80's. He wouldn't put a gun in your hand until you'd done a few months hand nailing everything. Decking, underlayment, shingles. You learn to use a hammer pretty quick when you're working by the square and there are guys with guns to keep up with. It sucked at the time, but I've thanked him since for bringing me up right, as I know now that actually costs an employer money initially.
No problem, Phillip. Here's the only practice you need- reach as high as you can on a wood wall with your off hand, up on your tippy toes. Then use the gun in your strong hand to nail your off hand to the wall.
Not only will this exercise bring to bear a specific set of problem solving skills, it will instill the appropriate respect for the tool.
More direct and to the point. Keep your Phucking thumb out of the way.
I've seen more than one guy have to take a staple out.
Bonus, they are hot and burn on the way in and until your flesh cools them off. not that you will notice they've cooled off.
You have safety glasses also, I presume?
(They are fun to run though)