I try to maximize productivity and efficiency; if I have a lot of time, I do something I'm less familiar with since I'll probably have to look things up and experiment, without losing state. If I just have a little bit of time, I work on the parts I know I could do in my sleep, so if I get interrupted it's no big deal, I can easily pick up where I left off.

But most importantly, I try never to procrastinate, although I don't always succeed... Good luck!