It's actually pretty straightforward. The only real trick is figuring out what the last person who did it did or didn't do.

I've had three twin sets and each one has been slight different in what fasteners were present in which places...and what kind of fasteners they were (screw/bolt head, etc).
I actually wrote up a sheet on this awhile back to help someone I was buying a twin set from disassemble so it could be shipped. It had been assembled for her, and she had no idea how it all went together. Let me see if I can locate that document and post it here. If not, I'll try to summarize to the best of my recollection. Stay tuned...