Ever see the old school bodymen work on a car? Some of their methods may seem primitive & brutal! BFH's, heat, prybars, jack-alls.
Yet the results they achieve can be better than what some of the newbies can do with all their fancy lasers & multi $$$ jigs.
When my Unc. & Dad had cabs, they employed 2 full time bodymen. Old school bodymen. They probably though that a laser was something from 'Star Trek'!
The way Eric described to align doors, with a floor jack & a 2X4, is a method that I've seen used many times.
Sure, it's 'Trial & Error'. Trick is, just do a bit at a time. Don't try to get the door aligned all in one shot.