If your uni is like mine, you'll end up teaching the same books for at least a couple of years. Instead of reinventing the wheel each year with new lesson plans, an easy way to keep track of your lesson plans is with Google Documents. It takes only a little more effort to write out my plan on the computer and print it out than if I do it by hand. And then at the end of the week, I just throw out the plan because I have it online. No more collecting papers for me. The next year, I'll do a quick search in Google Documents, find the lesson plan and do a few quick modifications. Usually, I'm pretty good at remembering what worked and what didn't from the year before.
A few tips:
1. Label things clearly. For example, I'll use, "Top Notch 2, Unit 1B" or, "Level 1, Midterm Exam Review Game" so as not to get confused the next year and waste time searching for stuff.
2. Plan things ahead of time. If you're the kind of teacher who scribbles something on a piece of paper 5 minutes before class, this won't work. Printers break, and run out of ink. The Internet is sometimes down. I usually plan 2 or 3 weeks ahead of time.
3. Don't be afraid to scribble all over your lesson plan after your first class. I teach the same class 5-9 times each semester. The first class is kind of like a testing ground and I almost always make modifications based on how things went.
4. Collaborate with your colleagues. We don't do this at my uni, but I wish we did. Imagine the possibilities if everyone used Google Docs and shared their lesson plans?