Last Saturday, I did pencil sketches based on prompts given to me from my Twitter followers (and others). I didn't have a theme, but one soon made itself apparent: animals! It was a lot of fun. I just may do it again sometime, as it reminds me that art should be playful and it is okay to step back from super serious ideas and stories...if only for a little while.
There should always be a sense of play in art making, an exploration of both your materials and your capabilities.