[strictly]

best trick is 2 people.

Once the door is on, then you can adjust it and fit it yourself, even using one hinge bolted up to hold the other but also by holding with your knee. 2 people is easier but you can adjust with one.

If you have forgotten your shim count, start with 1 at the bottom and nothing at the top, take your door b post catch off, and get your door lined up nice with the b post/fender/sill

If you get stuck take some pictures of the full door, with fender/wing, sill and b posts panel gaps

I am just fitting some new wings to a 79, and have had to do alot of panel adjustment of all removable items (boot, bonnet, bumpers etc) as the car was stripped down when I had first got it. Ive had to do it on a few 911's and it always takes me a bit of time, but it is satisfying to dial in those panel gaps, particularly with new wings which at first tend to look awful. I have found a trick with those, but its not what you are asking.