As a rough rule of thumb, if a web page reads coherently in a text-only browser, it ought to make reasonable sense to a blind user with a browser that renders text to audio. There's a lot more to it, though; and I for one will checking out the links that Fibula provided earlier. It's something that we all need to know more about, and -to begin with, at least, and so far as I could tell- it was quite difficult to get reliable information, or access proper test routines without buying software that small voluntary organisations might have found beyond their means.