Where do I start with Project Management?

I am a sole developer. I work on iOS apps and some RoR websites (and some projects incorporating both). I've been doing this for about six years and feel like I have a pretty good handle on learning languages and the nitty-gritty of making things work. SCM has been a revelation, and I'm learning that Git can be a useful tool, but I find that I am pretty aimless when I work on my code.

I decided today that I want to be a bit more focused, but also that I have no idea how to start managing my projects. My first thought was to write down everything that I want to do on a sheet of paper, but I'm interested in design strategies and principles, motivational techniques, how to come up with goals and deadlines, etc.

How does one start planning for a project?