For a new car I find it takes a couple coats to get it smooth, so I do an initial coat and then let it bake in the sun for a couple hours and reapply another one. After that, its just a maintenance coat every couple months. I use water droplets as my guide - big dime-sized droplets after a rain = good. Pea-sized (or none at all) = bad.
I use Liquid Glass Polish/wax. Amazing stuff, and i've used it for years on many cars - I've tried all of the other popular types, zymol or whathaveyou, and keep coming back to LG. It stays on for a long time and is very easy to work with. Its a little expensive at $25/tin but give it a try.