Well, some people include alternate style sheets for braille users. Basically, I'd say, don't use tables because they don't linearize correctly. Use a pure CSS layout. Put your content first, and your navigation afterwards. Take a look at it in a non-graphical browser, like Lynx, which will give you a pretty good idea how a screen read will read it. And of course remember to include alternative text for all graphical elements, which you should be doing anyway because it's a W3C recommendation and necessary for valid HTML.
If you don't have lynx, this Lynx Viewer comes in quite handy.