Proper full-blown exterior detail as from auto body (detailers might do something different but many many many of them have no clue about paint): Hand wash (I like Chemical Guys Super Bubble or whatever it's called), Meguiars cleaner wax, Meguiars Carnauba paste wax, then Meguiars Sealer 2.0. You're better off working one panel at a time so nothing becomes to tough to come off.
I swear, I don't work for Meguiars. I've simply never had a bad thing to say about their products and I've tried just about everything at the body shops as paint shop guys bring in samples and whatnot.
EDIT: Advice hint - If you're having problems getting the Sealer off, try just getting the removal cloth kind of wet. Soaking it will loosen up the sealer and basically leave the panel looking like you washed it without rinsing it. Just damp.