Pictures. Take tons of pictures... more than you think you need. They are extremely valuable when you're pulling something apart to see how it goes back together again.
Bag & tag. Parts that you're keeping, and even if you're going to get replacements, organize them, and keep everything together. I currently own 3 wiper motors (the original, the new one on the car, and the new one I lost along the way, but found after I'd bought and installed the new one on the car). Which brings me to:
A tracking device (spreadsheet, database, white board, et al). Whatever you need to keep things straight - use it! I have a spreadsheet I used for parts, including P/Ns, dates ordered, received, cost, quantity needed, and it all totals up on the bottom. The only things I didn't track were tax and shipping costs, which I'm sure would paint a somewhat different picture. I'm doing the same thing with my Jeep (literally, I forgot to track the tax and shipping, but it's too late to start doing that now... I'm almost done buying things).
You can also use your tracker to check-off (or add) tasks to whatever level of detail you need to get them done. Get a task done, check it off, and move onto the next one. Eventually, you'll finish. Don't do that, and you'll waste time going back to see if you did or didn't do something you think you forgot to do. You can also put your tasks in order, to ensure you don't wind up having to go back and undo something in order to do something else. I'm doing that on my Jeep as well, for instance: I'm changing over to H4 headlights and adding A/C, so I need to do those things before I install the new radiator, otherwise I'll need to pull it back out to get to those things.
Ask questions. That's what this site is for. I know I couldn't have done everything I did to mine without everybody's experience, explanations, pictures, advice, and even 'cheerleading' in many cases.
My main portion of the build spanned 4 years, and I'm still not 100% finished 8 years later. I still have some nit-noid things to do - I had hit the 'good enough' point and haven't made time to finish things up. In all fairness, I was under a time-crunch after I got it back from the painter (LONG story), but I made my deadline right as I hit the 'good enough' point. Now, I need to go back and do a few things that involve pulling part of the interior back out, along with a few things that I should've finished up along the way. But, I'm busy with my Jeep right now, so the good thing is that it'll be waiting for me when I can get to it.
Don't get discouraged. Depending on how big your project is, time will wear on you if you don't feel like you're making good enough progress. Take your time and do things right, don't rush, and don't look at someone else's project and think you should be going faster than you are. It's not a race, after all.
Mine was [literally] a pile of rust in the shape of a Mustang, with a seized engine, flogged transmission 'Fred Flintstone'd' floors, frozen brakes, broken steering column, no keys, no title, and no hope in too many peoples' eyes. One of the only positive things going for it was the fact that the tires held air. Yeah... it was THAT bad (my avatar pic is from the Craigslist ad I found - my signature pic below is how it came out). But, I had a vision, knew what I wanted, and all of the nay-sayers just made me even more determined to make them eat their words... and they did, along with a tall frosty mug of STFU. The Best In Class award at its first car show - the reason for the deadline - was WELL worth it. Also getting 'People's Choice' awarded by Ryan and Horny Mike was the best ever. Yeah, nothing motivates like a little bit of playground drama... LOL!
Hope this helps!