Another possible idea is to hold tournaments about once a week on the most popular games currently out...charge a fee to enter (between $5-10) And the winner gets a free game or free time to play at your gaming store. And you could occasionally have free tournaments (which would give a great image to your store)
Also for a place like this advertising is a must. One of the best (and cheapest) ways to do this is to make flyers and put them in mail boxes in the surrounding areas. And a good thing to put on a flyer like that would first time customers will get a free hour of gaming if they sign up to your emailing list...doing something like this would bring in lots of potential customers and if they like what they see they would probably come back for more and tell all their friends about it.
You could also put advertisement on your car (or your boss's or one of the other employees car) A basic website would also be helpful.
And have polls (once your store is up and running) about what your userbase likes for consoles and games, this way you could gage which games and consoles you should get more of.
These are just some of the off the top ideas I have....if I think of anymore i'll post em'
