What is your secret sauce? 
My first two attempts to answer this question seemed hopelessly egotistical so I'll try again, but part of consulting IS ego. This is my business model; there are many like it, but this one is mine. YMMV!
First and foremost, you must have the skills to pay the bills. You must be a superb troubleshooter and have a deep knowledge of hardware, networking and the Internet. You don't have to know everything, but your Google-fu must be strong. You must also acknowledge to yourself and to your clients that you don't know everything. Call in a specialist when you must.
Assuming you have the skills, you're not actually selling service, you're selling yourself. When you provide IT services to small businesses, you will be forming personal relationships with business owners and office managers as well as lower-level personnel. Abandon wholly any traces of the BOFH attitude, amusing though that attitude can be! You are providing a service that enables them to do their business, and in that respect are no more and no less important than a plumber or HVAC technician. Just as with those other tradesmen, your skills and knowledge have great value. Be confident in your abilities and manner, but not cocky. Be friendly, courteous and above all *professional*.
Once you've established trust, treat your clients with absolute integrity. Understand what they need and want, explain your thought processes (as much as the client wants) and advise them honestly. Use the appropriate tools for the job at hand; sometimes it will be a Microsoft product. Provide detailed invoices of what you did when, and how long it took.
Always remember that most people don't care about computers as such and see them strictly as tools with which to carry out their jobs.
I should also note that I did have the luxury of growing my business through referrals and word of mouth only; I've *never* advertised. And I don't particularly care if I get a given client. I never, never negotiate on price or accept services in kind. I didn't plan it this way, but I'm told by my business coach that this lends me a certain cachet, sort of like "playing hard to get." In my case, I'm not playing; I *am* hard to get. It seems to make my clients feel as if they're part of an "in-group."
And last but definitely not least, don't price yourself too low! Look at your market and your competition; don't be the cheapest. Don't necessarily be the most expensive, but let your rate suggest that you have skill, knowledge and experience.
Once again, YMMV. Good luck out there!