My best advice is to get in a little over your head. If you don't need to do research to finish your project, you're not learning much. Pick something you want to do but don't know how, and then just do it. Do your best attempt, then hit the books and Google and more knowledgeable people on the forum and whatnot when you get stuck trying to figure things out.
Necessity is the mother of invention, and invention is the mother of learning. Need some piece of test equipment you don't own? Build it! Improvise!
It is definitely fun to build projects like LED cubes, and it can be relaxing to work on a project where you know what you're doing (or are just following a kit), but the best projects make you learn.