So a 2003 DC crashed in a branch office. All it did was local authentication, dns, and dhcp. I have the server fixed now but I would think there is a few things I should do before I use dcpromo and put the server back on the network. What would be the right way to do this?
It's not clear whether you've re-installed the OS on this system; that's a big factor. The other question is whether you're keeping the same name on the server as it had before.
I'm going assume that you've re-installed the OS, and that the same name will be used. Correct me if that's not the case, and I'll edit the answer.
A lot of the cruft that you'd normally have to clean up will be picked back up by using the same name. That said, you'll want to clean up the metadata before doing the re-promote:
What this accomplishes is to clear FRS links, seize FSMO roles (confusion over those when the DC comes back could be ugly, though
That should cover it, take care of that then feel free to re-join the domain and re-promote.