5 words: Snacks and table top gaming.
The comic book store near my house has a side area specifically dedicated to people who just want to come in and play some games. They also sell games so I seem to pick them up pretty often. When you're gaming for long periods of time you get hungry, bam, a fridge full of sodas, tea, and water, and some chips or snack cakes, you're in the zone. You won't get RICH off it, but it's a good way to bring people in.
Like others have said, keeping booster packs and doing stuff like friday night magic can also really help. Maybe hold monthly tournaments, offer a prize, have a five buck entry fee or something.
Above all else, just provide good service. Even though I'm away at school for about 8 months out of the year, I prefer to buy all my comics from the shop back home. Because the guy who runs the shop at home is awesome and cool and cares about his customers, and the guy who runs the comic shop down where I go to school is like an older, grumpier, sexist, not as funny version of Comic Book Guy from the Simpsons.