My least favorite home-improvement-type job is installing doors. I hate doors. Door installations never go right. NEVER. Somehow, the alignment always gets screwed up somewhere along the line. It's astounding, really, how reliably murphy brings his love to door installations. ... Damned cats. Cats are the reason this door must be installed. So the door shall be installed, and then the small cat will stop bothering the big cat, and the big cat will stop pooping where he ought not to poop. (That is what must believed, as the alternative involves poop, and therefore shall not be contemplated) So now, it's off to home depot to procure said door. If anyone out there knows of a fool-proof way to install a door quickly, squarely, levelly, and easily, please feel free to keep it to yourself. :-) I make this offer because I assume that your advice will adhere to the following conditions:
1. It will make sense, and work perfectly in theory.
2. It will have been used by a respectable number of people who install doors on a regular basis.
3. It will not make proper allowances for walls that are out of true and floors that are not level.
4. It will not inconvenience you in any way if it goes horribly wrong. (and that's the main reason, really)
No matter what, shims will be required, and many of them. In the end, though, it'll work out, and all will be well. ... I just hate installing doors.