I used Duplicolor (who also owns Krylon) enamel from an autobody shop for the guitars and for a fork that I don't have any pictures of, and would likely use the same if I painted a frame. Lots of enamel vs lacquer arguments online...Google them to see some pros and cons of each. Get the paint off/rough up the surface, couple coats of primer, sand, couple coats of paint, emptied an entire can of clearcoat on each guitar, then sand, starting with 1000 grit and going up to a 2000 grit wet sand, being careful not to take off all the clear. Pay attention to the paint directions so you let the paint cure appropriately between coats. Lots of thin layers > less thick layers. Stay far enough away from the project when you're painting, because every time I get too close my paint runs and makes a mess. Don't buy a cheap clear because it'll have a yellow tint to it. And don't put lacquer over enamel unless you want the lacquer solvents to eat your enamel off and make a mess.

Powder coating will be the most durable, but it's not really a DIY job.