I have a door. It fell down.
How can I rehang it by myself? More specifically, how can I hold it up, a few inches off the ground, while screwing in the hinges?
In addition to the tips mentioned there, I would just add a few:
Take three pieces of 1x4 about a foot long and ripped one piece a little larger than the width/depth of the door (about 1 1/2in). Then nailed them together to form a U shape with the ripped piece at the bottom of the U.
This setup gives some support to keep the door vertical while attaching to the frame.
If you already know where the hinges need to be attached then you could remove the hinge pins, separate the hinge, attach the loose half of the hinge to the door frame, then get the door hinges lined up with the door frame hinges and put the pins back in.