For the spots that you're going to paint, sand it with fine sandpaper. Don't get it totally shiny. Then prime and paint just like you would anything else.
For the rest, unless it's in very bad condition sandpaper shouldn't be necessary. It will just create marks you'll have to polish out. Try buffing it first with a cloth wheel and buffing compound and see where that leaves you. Sanding creates a lot of work you'll have to do later. Protect it with a few coats of wax. I wouldn't bother trying to clear coat it. Unless you totally neglect it a waxing every couple months should keep it nice and protected. I assume this won't be a daily rider/commuter bike.