Make a list and write it down. Keep a notepad near the project, and another close in the house. Amazing how many things would cross my mind, and then I forgot because I didn't have a pad and pencil to write it down quickly. Lots of pictures during disassembly, and lots of bags and bins to keep parts sorted.
I've done a few and they are pretty exciting, and lots of fun, but learned the hard way to keep track of small parts when I had to buy a lot of small hardware I couldn't locate at the end.
Make a budget, and try to stick to it. I generally go over my budget by about 20-25%, and some I've heard go even further over.