I just took a class with House of Kolors Technical instructor, the mighty and powerful Brian Lynch. He's the guy the rockstar painters go to for help, advice, and working out paint plans. He has worked consulted for Trick My Truck, Monster Garage, and countless show cars.
He painted a guitar for me in the class with HOK's Orion Silver under a Orange Candied Metajewels, then cleared it in an open conference room(don't ask). Zero orange peel, better than factory from the big guys. It brings the bling.
A good gun helps, but a cheap one will do if it has the right tip size, sprays correctly, and is adjusted right. Also think about your air supply and how you regulate and filter it. With a cheater valve and not a regulator on the gun you will not have a constant air supply.
The old guns are a mystery to me, I only use and have read up on the HVLP guns. They are more efficient and create less overspray.
Here was his take on orange peel:(some of this applies more to 2k urethanes, mostly its universal)
1. Read, understand, and follow the tech sheets.
2. Spray a test pattern to make sure your gun is dialed in. Right fan size, right atomization, equal amounts of paint throughout the pattern, and a nice oval shape. Google it I'm sure you can find material on dialing in a spray gun. I bet DeVilbiss has it on their site.
3. Next you need to maintain proper distance with the gun. This will be in your guns manual. Typically my guns instructions say 6" away for a 6" fan. A guitar he recomended a 4-5" fan.
4. Next its all about laying down a single flowing coat of paint. Don't spray paint till it flows, spray so it will flow. This means a quick application of an even coat of paint. Your tendancy will be to put on too much paint. A guitar takes about 2 minutes to spray a coat. T
5. Leave it alone until it flashes. Don't speed it up, flash time is where the solvent gets out of the way so the molecules in the paint can lay down in a nice smooth pattern. This means don't blow it dry with the gun, don't super heat it, just don't. I know production shops do this on cars, but look at the peal they leave, because they are trying to emulate factory quality.(or lack there of) You are aiming for custom quality, so time matters less than quality.
6. Recoat within the proper times from your paint, per the tech sheets.
7. Buff lightly, enjoy. Don't forget to clean your gun.
Hope this helps, I know it helps me to type it out and think about the process.
*edit*
Finally, uploaded my pictures. This is straight off his gun.