I started out doing basic wiring jobs, a splice here, a joint there. My first "big" project was a mod for a Sega Genesis, that put standard av jacks on the back. Eventually, you will really get the hang of soldering, a basic skill for most of the projects here. Then, once you think you got that down, start cutting things up, like maybe find an old set of computer speakers, and see how much you can cut the amplifier before it doesn't work for you. Then fix it. Next, start playing around with modeling, and case building. Chances are, you would end up doing frankencasing, so do things that help you with that. Find an xbox, and fill in the ridges, polish it down, and give it a cool paint coat, or maybe do the same to pretty much any older console. If you can make that look good, you will become a frankencasing GOD.
Any of these could be a good first project, depending on what you want to focus on.