As a caveat, I'm not a game store owner and have no business experience. But I spend a lot of time and game stores and I buy a LOT of different types of games and had a friend who ran a game store. Here are my observations:
1. Be the friend of your customers. You can make more money in a month from regular customers who just have to own every product than all of the people who walk in off the street and buy one thing. Get to know them, play in some of their role playing groups. Let them play their home games in your store after hours. IMHO, these people will make or break your business. If they like you and are willing to come to your store, even if there might be a closer one or a cheaper one, you've got it made. They'll tell their friends, all of the people playing in their groups will come as well.
2. Provide gaming space. The more people playing your games, the more they'll want to buy. In the middle of your weekly D&D game and you need to continually borrow your friend's PHB? Walk over and buy one. Playing Magic and you just can't win? Buy some boosters. Just had a fun trial game of a board game? Buy a copy for yourself. I know a store in Australia that I was at that makes almost all their money from CCGs. They run booster drafts an average of 4 or 5 times per day. They have a dedicated player base though that will show up and spend the money on 30 boosters a day. Both the owners play magic though, know the cards and will sit down and play games with the customers when it is slow in the store.
3. Have books available, and when they come out. I can't count the number of times I've been to this board, and seen that people all over the country have been getting a copy of a new book and I've gone to the local store here and they've told me "We ordered it as part of our normal shipment which comes once every 2 weeks. So, we'll have it sometime within the next two weeks." Either that or "Oh, we ordered 4 of them in, but they sold within the first 2 hours, the next shipment will be next week sometime."
4. Pay attention to what your customers talk about and want. If people ask if you sell something a lot, get it in. If the majority of people in your store like movies, why not organize a time for all the regulars to go to a new movie as it is opening? Build a community of gamers. Partner with local gaming clubs to have their meetings or gamesdays in your gaming space if you have enough space.
5. Know what products are coming out, which ones are popular, and a bit about each game. Nothing turns me off of a game store more than walking in and saying "So, do you know when Complete Arcane is coming out?" and having them say "Huh? What's that?" when they have Complete Divine and Complete Warrior sitting on the shelf. It also turns card gamers off when you say "Sorry, I don't know what the card does, I don't actually PLAY the game."
6. Make the game store accessable to even non-dedicated gamers. When new people walk in, offer to explain the products on your wall, answer questions about what people might be interested in. Be ready to explain "What are Role Playing Games?"
7. Have a variety of products. Gamers are apt to switch games on the fly when their DM suddenly says "Oh, I've been playing this new game lately, you guys want to try?" Along the same line, introduce new products to your regulars. Tell them you have something new that you enjoy and made up two decks of this new card game and would like them to sit down and play a game with you so you can learn. They might just like it and buy a lot of it. Plus, gamers like to be able to get most of what they want in one place.
8. This one may or may not work, but it did for my friend who owned a store and the other store I went to in Australia: Stay open late. Even open late if you need to. Gamers, I've found will stay up until all hours of the night playing games. If you open at noon or 1 pm, then stay open until 11 pm or midnight, then you can have people gaming in your store until they'd go home anyways, to sleep. If you do this, then people won't think of you as just that place that they have to make a trip to once a week to buy things, instead it is the place they are playing Magic at on Tuesday, they are playing the SWCCG on Wednesday, and playing D&D at on Friday. They feel comfortable "hanging out" there, then they feel comfortable buying things there. I know there is a balance involved in this, it COULD get to the point where everyone uses your space to game but never buys anything. IMO, this only matters if you need the space for something else. If I walk into a store and see people playing Magic, even if it is just for fun, it's possible I'll think, "Hey, people play Magic here, I haven't done that in forever. Can I get a precon deck so I can go play with those guys?" By the same token, one of our favorite gaming stores had a seperate gaming space from the store and used to lock the store at midnight when he went home, then told us we could continue playing in the gaming space as long as we wanted if we locked the door on the way out.
Now, doing all of this takes a lot of work, especially if you try the "stay open late" route. If you have a family, it might be difficult to justify this to them. I think it would be possible to just do the same thing but open during the day.
Majoru Oakheart