If you are getting runs , its because a few things.
You have the material valve on the gun open to much, applying it to slow, to small of fan pattern,
overlapping you pattern to tight, low air pressure.

Spraying color isnt as easy as the pros make it out to be ...LOL

Base Coat / Clear Coat has made spraying paint alot easier as the base doesnt have to be layed real smooth as the clear is what gives it gloss, protection and smoothness.

Most high build clears today arent made to lay smooth as glass as they have developed them to have some orange peal as they found out that it helps cut down on sun fade.
The peal acts like a prizm and the UV rays might go in one direction but come out another direction.
a real slick paint job that stays out in the elements will fade faster because the UV rays go in and out at the same degee , this causing sun fade.

Supposedly PPG spent 100's of millions of dollars studying and finding this all out .

SprayTech