My driver'* door still sags a little from when I put it on, so I am going to have to re-do it at some point, and I was given this method as a suggestion:
If you have a garage or something with open rafters that you can get the car under, take two long ratcheting straps and connect it over the rafter and then down under your door at two points. This allows you to hang the door steady, and adjust it up to where you need to, while also allowing you to shut the door completely.
When I did my front, I used a jack under the back edge and I was able to get it close, but not perfect.
2007 Saturn Aura XR | 1970 Chevy Blazer 4x4 | 1970 GMC 3/4 Suburban 4x4