Contact the crew head of a theatre you've worked with and ask if you can help out during a hang or focus.
The next time you SM, pay close attention to the lighting designer during tech. If you have time, have the designer or an electrician walk you through the focus. Ask one of them to give you a sample of a "magic sheet".
When you're calling a show, pay attention to how cues run and what color choices were made.
After closing, if there's time before the light crew strikes and the theatre is empty, ask if you can play with the light board some and build your own "cues" to practice.
That's all things you can do on your own. Another thing you could do, if you had the time, is volunteer to be an assistant lighting designer for one of your colleagues (if you're not otherwise working during their tech).
Hope this helps,