Set up something to test spray on first.

You will want to move the gun side-to-side at an even speed...about 1 foot per second., and you should be about 6-10 inches from the surface.

Overlap each pass about half way, to start a wetspot, and keep it going.

Play with the test piece until you get a nice smooth finish with no runs.

When you can do that, then start on the car.

(This is a very short list of the hundreds of things involved in spray painting.)