If you need to generate leads for a service business, your most loyal clients will come from personal recommendations and referrals. Yellow page ads, cold calling and random web site inquiries will generate more "tire kickers" who shop by price. Consider reading some of the following books to help sell your services. Most of our development business (CD-ROM, web site, software) comes from word of mouth referrals and direct sales calls.
If you are a programmer/web developer you will find the greatest improvement in your business will come when you start thinking from the perspective of a business owner and marketer rather than a programmer. Spend as much time as you can studying sales and marketing materials. This will improve both your own business success and the success of projects you create for other businesses.
You should also build up a portfolio, a list of references and testimonials from satisfied clients to show others. A prospect's view of your ability to do a particular job may be determined by what they see you have done in the past. You will need to prove your credibility and your dependability. If you do not have a portfolio, start by creating small business sites for friends and family (just be careful to not do too many, otherwise you might wind up having to spend a lot of your valuable productive time when you start getting paying work maintaining those free sites that you did in the beginning).