You're in the paint booth, and you've used compressed air to blow dust from the panels, edges, beneath the mouldings and lights, and from the masking paper and the wheel covers ( You do this outside the booth first, then again in the booth with the exhaust fan running, starting furthest away from the fan). You then have washed the vehicle with a Final Wash or Prep Wash (other washes contain silicone which cause fish eyes). You finally wipe the vehicle with a clean tack cloth and you're ready to spray.
Occasionally, even after reducing the paint to the manufacturers specifications it may be too dense to spray properly. The usual specs is about 15 seconds in a #4 Ford viscosity cup. Translated into English, that means about 4 seconds to stop dripping off the end of the stir stick.
Turn your regulator to about 50 lbs, and get a nice oval pattern. Trigger the gun so that air passes through the cap, but no fluid comes through. Holding the tip of the gun about 8 - 10 inches perpendicular to the surface, start your pass along the panel at a hand speed of about one foot per second and squeeze the trigger to allow fluid. At the edge of the panel, release the trigger to stop fluid but still allow air. This constant air flow ensures that the air is not pulsing with bursts of pressure. This could cause excessive build up at the ends of you pass, leaving runs and sags. Don't stop at the edge of panels either, as this will also cause build up of material. On the back stroke, overlap half the first pass (the edge of the paint should appear dry, and the center wet. This is known as a medium wet coat), triggering the gun as before.
Always begin painting furthest away from the exhaust fan, so that you are painting over the over-spray. Otherwise, over-spray will settle onto the painted areas and may not blend in, leaving the surface dry and dull in appearance.
With base coats, wait until the coat of paint is DRY before applying the next coat. Otherwise wait until it is almost dry, but a little sticky (the directions are usually close). If you get runs, drips, sags, don't try and fix them while you are painting. You will likely create more problems. They are easy enough to repair after the paint has cured.