Some people sand between coats, some don't. I don't. If it's prepped correctly there is no need. The important thing- Make sure the spray paint has a fan nozzle, not one of those round spray patterns. I have gotten mirror finishes with black, and dark blue with duplicolor brand "body panel" (has fan spray pattern) paint. Auto part stores sell it, but so does wall mart (cheapest), and k mart. Also, it might help if you release the button between sprays. That will stop any running at the end of each spray, like alot of people get.
Steve