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First of all you need to define why your business is better that the 1000's of other businesses around. What is your experience? What can you do that no one else can? You should also join various business groups (chambers, etc) where you can network and market yourself. To get started in this kind of business you need to develop referrals.
Report Frank's answer
Start by talking to everyone you know. Do they need your services. Ask your professors from school. Run an ad in Craigslist. Network!
Report David's answer
Join your local chamber of commerce, community service groups, find a leads club. Expand your circle of contacts. People need to get to know you and trust you. In time you'll get a chance to share a tax tip, or they'll have an issue come up, and they'll know who to call. One of my earliest and best sources is an attorney who helps people start their businesses, and then he suggests they need a good accountant to keep them on track. Cultivate those types of referral sources.