One idea that some photographers use to exercise the mind is to publish a Photo-a-Day (PAD)  journal.  Over the course of one year, internet access willing, the goal is to post one photo that was taken throughout the course of a day, every day, for one year.

Personally, I have two reasons for doing a PAD journal.   First, it is a way to document your life through a series of photos.  No matter how mundane a photo may appear there is some meaning behind it.  The Second reason is to exercise my photographic mind.  It will force me into taking a new perspective, literally and figuratively, on the objects that occupy my daily life.