I think as others have suggested, you need to look at your local demographics and competition and find a way to differentiate yourself. It goes beyond what brand you sell, but the entire retail ecosystem you create. Remember that your competition isn't just the other bike shops - it's Walmart, Dick's Sporting Goods, Target, etc., too.
If I were to start a bike shop, I would consider having 3 or 4 brands, varying from affordable to high end. You might want to have that cornerstone bike brand that has a really broad range of products (Specialized, Giant, Trek, Cannondale, Schwinn, maybe Scott) offering something for everybody from the tykes to the local Cat 1 folks. Add in a couple of more specialized or boutique brands nobody else in the area is selling to provide some uniqueness. You also need to look out for the agreements with the manufacturers and distributors, so they don't prevent you from selling another brand you would like to sell.
Focus on service with a smile, and please, please, please don't be a bike snob. I don't know how many new cyclists I meet that get really turned off by the local shops when they are looking to spend $500-1000 on a bike, thinking that's a lot of money, and are treated like a second class citizen. If anything, embrace the beginners. If that actually involves hugs, so be it. lol! You've got a bike and they've got a butt. The more of those butts that you get on bikes, the better. Don't think of your customer base as a dollar amount - think of them as a community.
I think I went off on a tangent there. Sorry about that.
Travis Rassat
Vector Cycle Works Noblesville, IN
BikeFit Instructor | FMS | F.I.S.T. | IBFI
Toughman Triathlon Series Ambassador