Well, assuming you have a name, start brainstorming associations. For instance, if you're Joe's Restaurant, you would throw in visual concepts like plates of food, happy customers, napkins, forks and knives, dishes, a local landmark, etc. Then narrow down the ideas you like based on your business' personality.
Next, consider whether you want it to be iconic (with an icon), or whether it should be mainly text. To get something memorable and versatile, be sure that it looks good at large and small scales, and holds up in both full color and black and white. Would it look just as good on a business card as on a billboard? On an old-school fax printout as on your website?
You can also consider posting a contest for it on a site like 99Designs, where designers will compete with their designs and you'll pick the best one. Or, of course, you could always hire someone directly.