1. It's not the gun, it's the person. I used a 14.95 Harbor Freight non-HVLP spray gun in a jam and I actually really really liked it. Nice spray pattern and I did the same job as our expensive Devilbiss.
2. The compressor has a lot to do with it as well. Get one with a higher HP engine so it will not have to constantly run and run and run. A hot compressor is your enemy during paint because it may create condensation. A 220 compressor will have a good HP engine over the tank. 110 compressors will get the job done, just not as efficiently.
3. The environment is key as well. Clean and damp garage floor, clean walls, clean hands, clean towels. DO NOT get grease, wax, silicone or armoral near or on the car. Hello fisheyes and headaches if that happens.
4. Make sure you give the basecoats and the clear coats enough flash time between coats.
5. IMO one of the most important: DO NOT TRY AND COVER ON THE FIRST COAT!!! It will never happen. Spray nice even flowing coats, let them flash, then spray the 2nd coat.
6. Before spraying the whole car, buy a nice sealer and spray that over old paint/new primer. This fills all your sandscratches and prevents the paint from shriking on you. I will NEVER paint a whole car again without using it.