Mostly I make lists for projects. This can be daunting. Breaking something big into its constituent parts will help you organize your thoughts, but it can also force you to confront the depth of your ignorance and the hugeness of the task. That's OK. The project may be the lion, but the list is your whip.
I'm a lifelong movie addict, and one of my favorite projects is making replica props and costumes. Nearly every one of these - from R2D2 to Hellboy's revolver - ends with the paint job. And it's not just cosmetic. The paint literally tells a story: what this thing is made of, where it's been, what it's been used for, and for how long.
In theory, cars are fairly simple. If they don't start, it's either the fuel system or the electrical system. Teach yourself about the path of each in your engine and tracing it is fairly straightforward. But at the beginning, mastering each new system seems like an unreachable shore. The car is effectively a black box.