Wipe down with a plain rag to de-dust then wipe it with mineral spirits. You might want to use papertowels for the mineral spirits so you can see when it's dirty and youre not just spreading dirt and oil around.

What I've been doing is, wiping down with mineral spirits and papertowels (between coats, it might take 3 or 4 papertowlels the whole car, using about 8 surfaces on each paper towel), then let the mineral spirits evap (may take 20 minutes or an hour depending on temp), then before I'm going to paint, I'll go around it with a lint free cloth, slapping it around getting rid of anything that might have landed while the spririts were evaporating. Then ready for paint.

Between coats, the longer the better (to a point), one day would be safe in hot temperatures depending LARGELY on how thick the layer of paint was. It should definately not be tacky whatsoever when you're adding a coat to it.

I put a thick coat on Sunday night (I think), and it was tacky for nearly 24 hours. It dried with very little orange peel. I gave it about 48 hours to dry just to be safe.