Oh man I hear ya!!!
Thats my biggest problem too, just wanting to get the body/neck/what ever Im working on, finished.
Ive ruined many hour of labour rushing things and only now am I starting to learn from my mistakes.
You really have to be prepared to just spray one light coat and walk away for a day or two.
Brush on one layer and walk away. What ever it is you are doing if it isnt polyurithane, its gonna take time to get it right.
If the paint recomends 8 hours between sanded coats, leave it 16. At the end of the day, its only gonna look as good as the effort you put in to it. And that effort includes having enough restraint to 'walk away'.
In a months time when your playing you shiny new look guitar youll forget all about the hard work, so trust me its worth it.
Good luck.