Throwing in my bit of advice - I worked in my FLGS for a little over a year. Some of these might be a bit tricky to do when first starting up, but they're worth considering as your business becomes stable (and hopefully grows).
Research - go to the other game stores in your area. Looking at their customer service is important, but consider other elements as well. What do the stores carry? What do they not carry? Is there a possible niche your store could fill? Geography is important - if all the stores in town are on the north side of town, put yours in the south. The suggestion someone had for paying a friend $20 to be a 'secret shopper' is great, but I'd go a step further and have two twenties handy; one for a male friend, and one for a female friend. I'll bet anything you get two very different experiences from them, and I'd pay close attention to what your female shopper has to say.
Environment - Please, for the love of your favorite deity, make your store a place that you'd feel comfortable bringing your grandma. Despite persistent rumors, all gamers are not social misfits in their mid-20s with hygeine issues. About half of our customers were under 15, and coming in with Mom and Dad. Mom and Dad do not want the first thing they see when they walk in to be the Book of Demons, or the latest underdressed, overbosomed comic issue from Mad Cow Comics. Certainly, you can stock these items (and should if there's a demand), but 'strategic product placement' is crucial. In the store I worked in, we maintained a strict "PG" rating - customers who used profanity or held loud discussions about 'uncomfortable' subjects (sex, torture, demon summoning, etc) are given one warning, then asked to leave.
Make your store look inviting. Much of this has been mentioned before - clean, well lit, and open. Don't cover up the windows - porn shops and crack houses have covered windows. Posters and murals are nice, but choose wisely - Spiderman good, Lady Death bad. Elminster good, Orcus bad.
'Regulars' - You want regulars, and you want to keep regulars. How you do that is up to you; we sometimes give small discounts to people who we know buy a lot of stuff. But be careful- keep a list of who's getting what discount, and why, and how much they're buying. Prior to my working at my FLGS, they had a problem with this - the old manager gave out too many 'permanent' discounts to too many people, and we had no idea why. We ended up wiping the slate clean, and cancelling all discounts until we could review the situation on a case-by-case basis. The majority of our customers understood and were fine. Sure, we lost a couple of people over it, but you know what? When we checked, those people who were upset were the ones who hadn't bought anything for months or years.
Another thing about 'regulars' - it doesn't mean 'co-owners'. Some people, when they become a regular, get to thinking that the rules don't apply to them - this isn't because they're malicious, but a natural consequence of being comfortable in an environment. We've had regulars who suddenly decided they could walk behind the counter to grab things, or began swearing a blue streak at their computer game, or insisted on regaling every new person that came in with tales of last night's D&D game when they killed all those demons. Don't be afraid to take these people aside and talk to them - I found most to be perfectly willing to fix the problem themselves - or take more serious steps if needed. I guess the main thing is keep your regulars, but not at the expense of your other customers.
Employees - I hate to say it, but in some ways gamers can make bad game store workers, in the same way that they can make bad owners. If you open a FLGS, you will get all kinds of applications from people who think it would be 'cool to work in a gaming store'. Most of these are basing their opinion on those stores they've seen where the employees ignore the customers while playing games all day. You want to weed out most of these, and find the real gems; people who actually want a job. The ones who know that work involves, well, work. That realize that running a gaming store isn't about playing games, but about endless cleaning, reorganizing, customer service, etc. The owner of our FLGS is one of those 'gamer first' types, but fortunately has the good sense to realize it, and hires competent employees, and a manager who does remember that it's a business first. With these people behind the counter, he can concentrate on shmoozing with the customers, which is where he excels.
Oh, and if you can find these employees - pay them. I've seen too many stores fold who paid their employees minimum wage or less (half money, half store credit). This does not encourage good customer service or a strong work ethic. When I can get $8 an hour at McDonald's, why would I settle for $6 at your place? Obviously, this is tricky when you're first starting up and money's tight, but IMO one good, happy employee is worth 2-3 bad employees.
Events - I'm firmly in the 'in-store events are good' camp. In fact, after we cleared out the discounting problem I mentioned previously, we went with an 'event-based' discounting plan. If we held a Warhammer tournament, everyone who signed up got a card worth a 10% discount on all Warhammer and related products (terrain, paint, etc) that was good from the time they signed up until about a week after the event ended. It increased sales of those products and improved attendance at events, and it set a limit on how long customers could use a discount. The biggest problem can be space management - it is possible to have too many things going on at once. Currently, my FLGS has RPGA once a month, Vampire LARP once a week, Magic Tournaments once a week, Pokemon and Yu-gi-oh leagues once a week, and Mage Knight once a week. They also run a couple of store-sponsored RPGs (including a 3E game specifically for 15 and under, to encourage new players getting into the game), and a few independent RPG groups. These are all run with little to no employee effort (usually just keeping score in a tournament) other than scheduling (like on the Saturday the RPGA comes in, we either cancel the Magic tournament or play one of the less popular formats like Type I or Type II).
If you have in-store gaming, develop an understanding with them. These people are like advertising to you; people come in and see people playing something interesting over in the corner, and they'll ask questions. Encourage the people playing in your store to be willing to answer those questions. But be careful about that 'comfort' factor - at one point we started noticing that all our 'new' Warhammer books had creased covers, and quickly found out why; people were taking them off the shelf and consulting them during play, using them to build their armies, etc. Obviously, we had to correct that problem.
Product - Obviously, you'll need to decide for yourself what you stock. But make sure you know where people can get what you don't stock. I'm not talking about special orders - you should do that - I'm talking about things that may be tangentially related to your business. At our FLGS, we'd get calls from people all the time asking if we sold coin-operated video games, or bingo supplies, or fancy chess sets. We made sure we could give them the name and number of whoever did sell them in town. Maybe you'll never see the person on the phone again, but you leave an impression of being knowledgable and courteous.