I keep a legal pad with me and make notes as I refine a print (exposure time, f-stop, dodging and burning with sketches, etc., etc.). When I've made a final version, I transfer the information to a computer file for future reference.
As for keeping track of different versions of prints while working: I have a magnetic white board that I hang prints on for evaluation. I make notes under them with a board marker during the refinement/comparison process. When I do different things in one batch, I bend corners on the print. There are enough corners and combinations (one corner, two corners, alternate corners etc.) that I've never needed more than this.
I have tried marking tests with a Sharpie, but it often dissolves away in the fix. Soft pencil on the back stays but is often harder to read. For me, the corner bends (or clips if you like) work best.
Doremus