When you're hunting for them.....what are you doing when you find them? There lies your answer. They are pretty cover specific. Not in long grass if they can help it, more towards the scrub bush, small trees and light grass
When you bust into a covey, take one or two if possible and then try as hard as you can to watch where the majority of them flew off to. Then, take your dog and work the cover hard in the general area they went to. Hitting up the "singles" is usually productive and even with wild birds...they hold tight and bust out from under your shoes. Good luck!
Finding good quail cover, as has already been stated, plus a good dog will result in more quail on the ground.
One of the most frustrating part of quail hunting is that they always seem to have an escape route that provides you with little/no shot. Knowing which way they're going to fly is often times the most important part of the hunt.