Wear comfortable clothes that don't have metal zippers or snaps on them while you wash your ride. You don't want to scratch your paint when you're leaning up the side to reach the roof -- especially if your ride is a big truck.
Forget to take your jewelry off before you start washing. If you wear rings, watches, necklaces, a belt, or anything else that could potentially scratch the paint -- leave it inside. There's time enough for style when your ride is clean.