There's a ton of VERY useful advice here already, but I have a few tidbits that haven't been mentioned yet.
- For discounts, give a coupon for X% of today's purchase as store credit towards a future purchase- and make sure the coupon has an expiration date! One local store, that I go to regularly to browse, ALWAYS gets me back to BUY at least every six months because of this. With every purchase I get a coupon for 10% of what I spent as store credit to use however I want. And then when I use the credit (and of course, I always spend more than the credit) I get another credit coupon that's good for six months. It's a neverending cycle. So even if I'm temporarily distracted from gaming, I'll see the coupon on my fridge with that expiration date and I'll HAVE to go in- otherwise it's like throwing money away!

If anything the store should cut the expiration date shorter, then I'd come in even more often- even though the store is kind of out of the way for me.
- KNOWLEDGEABLE, friendly employees that go above and beyond to make me feel like a valued customer. One poster mentioned an employee that offered to call him back when an item he was looking for came in- that's the kind of service you need. They also mentioned offering someone who's been browsing awhile a drink. That too is the kind of service you need. You have to make people want to give YOU their money rather than Amazon, or any other online option- especially when they will often have to pay more for your books than they'd pay online. Let's face it- you'll probably never be able to beat the deals they can get online. So you have to give them the face-to-face good service no online store can offer.
- Atmosphere: The other thing you can't get online. Try to make your store "feel" like the kind of place your customers want to return to. You'll have to judge that for yourself based on your area and the population, but alot of it can be inferred by what you'll sell. If you focus on fantasy games, have a suit of armor on display or mount one of those cool dragon head masks to look like a hunting trophy. Have swords displayed on the walls, and have some for sale. If you have more sci-fi products, have enough spaceships models hanging from your ceiling to re-enact a planetary assault. Or just go for general geek appeal (be honest- that's who many of your customer's will be)- put a large rolling ball sculpture on display in the window, recreate the battle for Helm's Deep in Lego, or display cardboard cutouts of 7-of-9 and "slave girl" Leia. Or do all three and then some. Contract a local SCA armorer to make chain mail items for display/sale. Heck, have him sit in the corner on Thursdays and make chain mail in the store and teach others. Have your employees dress as a movie or book character and give a discount or free mini to whoever can guess who the are. Better still, offer a discount to CUSTOMERS who shop in costume! (but only on special days- you don't want your shop to turn into some creepy Furry hangout!

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In short- be interesting! Be the place I WANT to come back to even though I can get the book cheaper online. Whether it's because my credit coupon is about to expire, or I don't mind the extra cost/bother because I like the service, or just because I want to see what new interesting "whatever" you have displayed in the store- make YOUR shop the place I want to shop.