I know a friend that owned a comic/gaming shop for a while and you're in for a rough ride. It's a fun job for the most part and you'll make some awesome friends, but just know that those places rarely survive. After a very long run, my friends place finally died a long painful death that would make cancer patient cry. Just be careful with your money.
Now that we got that out of the way, you want several things:
1) A place for table top gaming like Warhammer. You don't necessarily have to sell much of those, maybe some painting supplies and the likes, but just have a space. Let people bring stuff in and maybe even store (have a locked room or some place you can even display their locales). This will be bring in fairly loyal customers who will eventually buy very expensive things if you have them.
2) Have an area with tables set up. On these, let people play games like M:tG, Dungeons and Dragons, board games, or anything else. Most importantly, don't charge for this space. If you charge, they won't come. If you don't, they will come and hang and spend money. Cater to these people and stock what they want and they will bring in a decent cash flow.
3) Have decent computers if you have the money. Put great lan games like CS, TF, BF, Warcraft, Starcraft, and whatever else people play over LAN (I haven't played LAN games in years). Just make sure to keep these fairly up to date.
4) Have a decent TV with your gaming consoles, don't skimp here. You can build a cheap computer that run a lot of game and nobody will notice, but you should have a nice TV.
5) Have at least one 360 and make sure it's connected to Live. Have games like Halo 3, Guitar Hero 2 (Rock Band soon), and Gears of War and it will do good.
6) Have a Wii. This is the kind of place Wii's were made for. Just pick any *good* multiplayer game (not Metroid Prime 3) and you're set.
7) Have a good pricing policy for your consoles and computers and stick to it. Don't be a jerk, but enforce your pay by the hour or day or whatever you plan to do.
8) Have a security system. This sounds like a no brainer but lots of people miss it. Have cameras in your store (and actually turn and keep them on) and have alarms set up. People will try to steal kids M:tG decks and people will try to break into your store.
9) Be in a big enough city to support your store and find a good location that can be scene. The closer you are to a school or WalMart, the better you are. If you're in some little dump of a strip mall, you'll go out of busniess.
10) I have no idea what you officially need to play those games, my friend just supplied the system and games. I have no idea if it was legal or not but that's what he did. Are there any similar places in your area? Ask them.
