1. Recognize your skills and limitations. What you can't do will have to be farmed out and paid for someway--cash, trade, barter.
2. Know your financial situation. A project will cost more than you think. Many a project has been sidelined or uncompleted due to a lack of funds.
3.Orphan builds. Better to leave the orphan brand builds to the more experienced folks due to the lack of parts availability. Finding doors for a 1927 REO or a trunk lid for a 1925 Essex for example. A lot of the more experienced guys will modify something else to fit or scratch build a part, not everybody has that talent or the means to do it. Lots easier to find parts for a Model A Ford than a Kaiser-Fraser. Start with the most complete vehicle you like that you can afford. If you have to wait a bit to get a more complete one, you will be ahead in the long run.
4.Have a vision. Draw it on paper, copy pics of other builds with things you like, if you have to, cave man and use sissors, paper, and paste to put together a pic of your vision, then build it. Don't change designs in the middle of the build, have a plan and stick to it. Small detail design can and will change, but the overall picture should remain the same. It's a lot easier to build something than it is to build part of it, tear it back apart and then start over.
5. K.I.S.S. {keep it stupid simple}. Leave the complicated suspension systems, trick engines, and general fancy stuff to the more experienced guys. A simple leaf spring or coil over suspension is easy to figure out, a mostly stock engine will have plenty of power, and you don't really have to have a electronic gizmo to work everything. A simple stock drive train will still be fun in a lightweight car or truck, and will not be as much a bear to keep running. Leave the diesel's and race car engines alone until you get more experience in proper set up for them.
6. Have fun with it! If it's not fun, it's work. When it turns into work, you won't want to mess with it, and it will sit. Nothing wrong with taking a break to prevent burnout. If it's not fun, do something that is fun for a while. The build will still be there for you.