Offline, finding out what your customers want is a matter of looking at your records to see what's selling best, asking customers for feedback, and asking your employees to write down things customers ask about that you don't sell. When you see trends, look for ways to add the most requested products or services to your offerings and feature them in a way to make them prominent to your customers.
Online you can do something very similar. Use web analytics software to analyze what pages visitors are looking at on your site and how they move through the site. Determine which pages are most popular, and seed them with ads for related products (your own products, or products you promote as an affiliate.)
Where do you get web analytics software, you ask? Your hosting company might include use of a web analytics program as part of its service. If it doesn't, Google offers a free analytics program called (surprise, surprise) Google Analytics. To use it, you just have to insert a small piece of code on every page of your website.
More: 6 Ways to Find Out What Your Customers Think
