First:
... don't.
Second:
Find your niche. Every hobby game store that survives has one. For example, locally, we have:
1- 401 Games: A local convenience store that turned into a CCG store by accident. . Their schtick? Cards, space to play, cheap mainstream RPGs. Lowest prices in town. It is
always cheapest there. They depend on volume.
2-Hairy Tarantula: Traditional Hardcore RPG Game / Comics store. A comic shop that became more focused on games over the years. Their Schtick? Large RPG inventory including a lot of more obscure titles. Has lately been focusing more on boardgames though. Reason? That's where the money is.
It has not helped that their three seasonal sales are predictable enough and significant enough in savings that people find themselves not buying for two months to just wait for the 30%-40% off sale in two months time.
Sales are good. Regular predictable sales that come more than twice a year are a bad idea, imo.
3- Dueling Grounds: Card and Miniature Store. Lots of singles for sale. Their Schtick? Large brightly lit area emphasizing 800 sq, feet of on site play space. A *lot* of tournaments. Every week something new.
Another store cloned this model and offered painting areas (and paint!) emphasizing War Machine. Otherwise, a clone of the other. It's a big enough city and the stores are far enough apart that it works for them.
4- Gamerama: Miniatures and used DVDs and Computer Games. Their Schtick? Empty used games and DVD boxes accessible to customers. All packaged product behind a long counter running 60 foot length of entire store. They have virtually no losses due to theft.
Brisk used computer/video game business has a lot of product turnover with high margins. New games sold as they have to - but the money is in used games. Miniatures business is extensive GW as the profit margin is obscene.
I could tell you stories of the general hobby games stores too. They open from time to time. The problem is - they close just as often. It's a tough retail business to be in. Whatever you do - you need to find your niche to survive.
Third:
You are running a business. You need to sell products that sell well with reasonable return. Right now, that means: CCGs, Collectible Miniatures, Boardgames and toy figures.
RPGs, you see, are available online in pirated versions for free. That's a price you cannot ever meet. Others are sold online as well - at a price you cannot ever meet. While you can sell some of that product line, concentrate on WotC product lines and avoid stocking too many products that don't sell. The generalist hobby store / comic shop has not fared well under internet competition. Carrying too much D20 inventory is death.
Fourth:
Most of these ventures fail. Thinking yours will do better is probably dead wrong. Finding a reason why yours won't - and pursuing that vision with clarity and purpose is important. If you aren't where you want to be within two years - you probably won't ever get there. Get out while you can.