A bunch of really good ideas here:
http://www.thehighroad.org/showthread.php?t=471029
IMHO, the best trick is to find a niche. What does your shop do that WalMart doesn't and "Fred & Ethel's Guns & Bait Shoppe" accross town doesn't do. And what kinds of things to folks really wish they could do/see in person?
I'd say a wide variety of holsters, good concealment holsters in lots of styles and from really respected makers, would be great. And figure out a spot and procedure for letting folks try them out with their guns. (A lot of planning goes into making such a thing safe...) Actually getting to handle and try on a selection of holsters might help a lot of us avoid the infamous "drawer full" of slightly used holsters we all seem to collect while searching for a good one.
Maybe discreet concealed-carry oriented clothing, too. Everybody likes 5.11 pants and "shoot me" vests, but concentrate on nondescript, non-attention-grabbing clothes that will obscure a sidearm. Something like this, maybe:
http://www.bullfrogskin.com/
A good selection of handgun grips might be a nice addition. Offering to install while they wait would be nice touch.
If you can form relationships with local gunsmiths and leather-goods (or Kydex goods?) makers, grips makers, etc. where you can cross-advertise, and maybe even have them do demos/visits, that would be really cool.
IMHO, hunting gear is just a tapped out field. For every 100 deerslayers who wander around trying on camo coats and Realtree boots, 99 of them will go home and order it on sale from Cabela's anyway.
On the other hand, a KILLER selection of reloading components will draw folks from miles around. Especially heavy stuff like bulk cast bullets, and expensive to ship items like powder and primers. If your prices are good, those will fly off the shelves. If you have stuff IN STOCK...ALWAYS...LOTS...you'll have a very regular customer base.
Above all, I'd say be EXCEEDINGLY professional in every aspect of the front end of the business. Make the store bright, clean, and organized. And inviting from the exterior, too. (A lot of gun shops seem to go for the abandoned warehouse look. Yikes.) Get shirts & gear for your employees that look positive and upscale. No blaze orange, no camo. Business casual, good grooming. Employees must be polite, cheerful, helpful, and honest. ("I don't know, but I'll find out," should be your employees' default answer in place of any speculation or half-baked opinion.)
Make the shop the kind of place that your grandmom would stop by on her own without an escort -- and be happy she did.
Anyway, good luck, read that other thread for some even more in-depth responses. And let us know how it goes!
-Sam