How do you do what you do? You have experience, a track record, past successes that you want to relate to your customers. Especially if you're selling a service, make sure that you put down your background, past clients, or samples of your work. Chances are that you're not the only one offering these particular services, so toot your own horn a bit and show customers what you've already accomplished so that they can see what you might be able to accomplish for them.
So now they know who you are, what you do, where you're located, and how you do what you do. But why should they hire you? You probably don't do or sell anything that's never been done or sold before. That's where the Unique Selling Proposition comes in. A Unique Selling Proposition is a brief, catchy message that explains what makes you different, and why you are better than your competitors. Like everything else on your site, your USP should be brief, easily found, and repeatable.
There's a whole lot of stuff going on online. Peoples' attention spans have gotten shorter and shorter. The crux of the website is to get to the point quickly and make it appealing and interesting. You can do a lot of fancy things with a site — flash, sound, video, blogs — but you still have to shout your main message loud and clear.