Glocks would be a good start, but don't fall into the trap of recommending them over everything else. Sell the customers what they want, not what you want them to have. I have a friend that owns a gun shop and if you walk in and ask for a Sig all he will do is tell you how great Glocks are and why you should buy one.
Here is what I like to see in new gun selection when I walk into a store:
60% Value Priced guns- not cheap but good values like Ruger and CZ semi-autos, Kel-Tec pocket guns, used S&W and new Taurus revos, Savage centerfire bolt actions in a variety of calibers, Mossberg Shotguns, CZ Rimfire bolt-actions, Marlin Lever guns in popular calilbers like .30-30, .45-70 and .357/.44mag
30% Premier guns - RemWinRugerCZ bolt action centerfires, Glock/Sig/Beretta/Springfield XD semi-autos, S&W and Ruger .357/.44 mag revolvers, Ruger 10/22 target models, Springfield GI series 1911's, Remington Shotguns, Bushmaster AR's
10% Showcase guns - Colt/Sig/Springfield/Para-Ord/S&W 1911's, Old collector type S&W revolvers, SA Revolvers (could also be in the premier line), Colt AR's, Benelli/Beretta shotguns, conversation pieces like a .500S&W Mag revolver, .50BMG Bolt-Action, etc.
On the new guns, don't compete with Wal-Mart. Don't sell standard Savages for $75 more, don't sell the Remington 710 or the Mossberg ATR 1000, don't sell Remington 870 Expresses, don't sell standard Ruger 10/22's, you get the idea. Be honest with the customers and tell them that Wal-Mart sells it cheaper than you can buy it. Encourage them to come back for the accessories that Wal-Mart doesn't sell though.
On used guns, if you can't sell for $50 less than Wal-Mart, don't buy it. Otherwise, price them by what YOU would pay for them. Don't put $250 on a regular Marlin 336 in .30-30 with the safety when Wal-Mart is selling them for $269 + tax.
Used guns are money makers if you are smart.
$10 transfers
Clean, well arranged quiet store w/o pushy sales people. I was very good friends with the guy above and all but refused to buy form him becuase of his attitude and sales tactics.
Have a good selection of specialized ammo for hunting, personal protection, cowboy action, etc. Don't focus on practice loads for common calibers. Keep a good selection of mil-surp calibers.
I know this is long, but I think it is fairly representative of what most people want.
W