Clay bar is the way to go. After washing/drying is the best time for clay. There are light/medium/strong clay bar, the strongest are used with a lube, light used with plain water. For over the counter, Mothers clay bar/lube works great. It will not remove paint or scratch if used right. The clay is a sticky substance that pulls "fall out" from the paint making very smooth.
Tip* Break new clay bars into 3 section, work with 1 piece at a time.
If the clay bar falls on the ground throw it out. It will pick up anything on the ground, you might as well start rubbing with sandpaper . . . . .
Very good time for a polishing & waxing after clay bar.
Always work on a cool car out of direct sunlight
Work 2' square areas
Spray lube
Rub clay on wet area - no need for pressure - back/forth not circular!
Buff dry with soft towel - microfiber best choice
Continue around the whole car.
http://www.topoftheline.com/tolae/
Best way to feel before & after
Put your hand inside a plastic baggie rub gently in a small area before & after clay bar. You will be amazed!