One of my all time favorite quotes:
"In preparing for battle I have always found that plans are useless, but planning is indispensable." - Dwight D. Eisenhower
I don't know what your exact project is, but it's the same for anything - from cars to cabinetry. Get a plan, not a vague idea. Spend a day just sitting and looking at your car with a pad of paper. Think things through and get a very good idea of where you want to go and how it's all going to fit together. Write down info, decisions you need to make, and questions you need to ask. Try to get an idea of what will have to be done before others and what can be done anytime. AND do you want to be able to drive it as you work on it or is it going to sit until it is complete? Me, I like to section my work so I can drive during the summer and break it down in the winter. For that reason, most important to me is safety and driveability.
If that seems like to much, think about each area and what you want to do with each first - suspension, brakes, steering, frame, ride, body, drivetrain....etc, etc. Then sit back and pull it all together.
Also stop every once in a while and think if you are being realistic. After you have a plan, recall you have a budget, and decide what is going to fit into it, now and later.
When you are unsure what to do next - clean something. You'll figure out something to work on shortly.
