I own a shop too and it's not an easy business to start. I've been at it a year (opening our second store) but I've been with this company for 4 years. They've been around for 12. I think I've been doing well because we are already established and our other store eats almost all of my overhead, which as techs said is a big deal, ESPECIALLY during slow times.
Know this, there WILL be slow times, sometimes a month or more. This is a feast or famine business so it's imparitive you plan ahead for that. Track your hours and use that first year as a guidline for the years to come. that also helps because it sets a benchmark and as your business grows you can see tangible growth.
Your first year will be very very tough. Even for me, established as we are, this first year has been pretty tough. I lucked up because another small shop in the area shut down and I bought out his customer base. Without that I'd still be struggling. I've also just now started seeing steady repeat customers.
Your customers are everything. Word of mouth will make or break you. Good word travels slow, but it does travel. Bad word of mouth travels at light speed. Granted you will get that customer that you can do nothing about and will get upset, think you ripped them off, think you screwed something up and no matter how hard you try they will never be satisfied.
The BBB and Chamber of Commerce are a necessary evil and you must make them your friends.
Establish your business to a point where it's autonomous enough that you can bring in a part time guy to watch your store / do repairs so that you can go out and hit the pavement.
Come up with a fee schedule. You'll want a minimum bench fee/diagnostic fee. You'll want a flat hourly instore rate. Call other local shops to guage what you should set yours to. I also set a seperate rate for component laptop repair (i.e. if I have to crack the thing open vs. a virus clean or format reload). Finally your onsite rate should be fairly high because in the beginning it will be you doing it meaning a closed store.
You want to diversify. Do not just be "Joe repair shop", be a total solution provider. If there's something you want to offer and can't find someone in your area to partner with (Apple repair, web design, networking, cable running, etc.)
Used PC's have also been an excellent source of revenue for us.
As techs said you MUST get a yellow page ad. I'd give a number that will ring to you 24/7. Take calls at 9pm or 2am if you have to. Turn down no job. Consider yourself on call 24/7.
We also do really well with contracts. We sell in blocks of ten hours to customers who need an "IT guy" but not full time. Doctors offices, lawyers, accountants, professional people are a good candidate for this.
If you have any other questions just post and I'll try to answer.