When I was spraying the guitars I was building (with spraycans, dont have a compressor), I had problems with runs and having to hold them still, tried all the tips in the books, but I still ended up trying to hold the guitar while I sprayed it. What I wanted was something that held the body vertical to spray, then flat after I had sprayed the top and back, so I could a decent coat on and not have runs.
So I built myself a rotisserie....

That was a bit rough so I made a refined version

This is the other end, I built a handle so I could rotate the body without touching it. The wing nuts on the threaded rod act as a clamp once I had finished and kept the whole thing stiff or loose, depending on what I needed.

I found I could spray both the sides when the body was flat, then tilt it so the back was vertical, then 180 degress to spray the sound board, then lay the sound board face up, so I got no runs.
It worked pretty well for me, obviously a lot less sophisticated than some of the paint shop jigs I have seen on the forum, but hopefully some of the less well equipped might find this useful.
It probably cost about $20 in threaded road and wing nuts and $1 of scrap ply. It folds away and hangs in the ceiling!
Cheers
Richard