If you want to make real money, stick the the Pyramid Principle. "There are more people with money to spend on the lower end of the price scale, than at the top."
I'm sure you've done some research and know what the surrounding stores offer. Next, BE VISIBLE. Don't rent a store at a cheap rent in an out of the way location. You can not spend enough money on advertising if people don't see you.
Next, offer some high end products to test the waters. There's bigger margins here. If it works, increase the line. Ask the manufacturers to work Co-Op advertising deals with you. Some will. Some won't. But either way, you must convince them why they should.
Lastly, make your war chest has a heavy advertising budget. You need to advertise heavy in the beginning to get your name out. Do quickie 10 second radio spots with programming geared to your target market. If your selling ipods... that is a way different radio station. Figure at least a modest $10,000 in media advertising in the first 6-8 months, minimum, if you want to do it right. Don't take short cuts. Hire quality people. And finally, be honest with your customers and yourself. Good luck! :)
