Here are a few more suggestions for staying fresh betwen auditions or projects:
Learn a new monologue.
Find a few new scenes to study, then prepare them for performance, possibly putting yourself on “tape” for review and analysis (this might require participation from a friend or two, so stay social).
Work on your voice.
Read screenplays and plays.
Read a book or watch a DVD on the craft.
Help someone else with their project.
Start a screenplay reading or play reading group and meet weekly for reading and discussion.
Practice remembering extraordinary events from your past, the highs and lows, and keep those memories and the feelings they produce fresh for access when needed.
Do something new.