While Ty has talked about products and such, I'd just add (besides what he said about adequate thinning) to use good technique and practice. Set up some panels (old fuel cans or other smooth surfaces) and practice with the gun. See what happens when you change the fan or the air or mix. The biggest issues is usually learning how to best use the equipment and that just takes practice. Things like holding the pattern at an even distance, not tilting the gun and learning how long you can hold in one place with various materials before you get runs. All that is just practice and knowing the equipment. Don't expect a 20 point finish the first crack out of the box, Just learn and get better with the equipment and technique as you go along.
If you have specific questions, just ask here.