4) Have the guns out so people and pick 'em up, hold 'em, play with em. The BEST setup I've ever seen was at a big box hunting store. ALL of the rifles were on a wall. They each had a gun trigger lock and were cable locked to the wall. But you could go up and hold and cycle the action of all the rifles. It was a beautiful thing. I HATE having to ask permission to see this gun or that, and not being able to read the small print of what it is or how much. And the employee is always bothered by my being there wasting his time.
5) Have the prices CLEARLY marked with large bold print. No squinting.
6. Don't kill yourself trying to stock all sorts of stuff that is going to be a hard sell. Too many holsters and other accessories is a waste. I know we all want a selection but it isn't realistic to carry 4 different holsters for every gun. I'd rather see more gun selection.
Sorry if that seems like a rant, but it is very important. Many businesses in my area lose a ton of money due to their reputations for having rude employees.
You have to carry things that people can't buy online or the first you'll hear is I can but it cheaper there. But they want you to carry it so they can look at it and take up all your time. Then figure you can give it away.