My students' first shooting assignment is called "Stream of Thought" : Pick a subject and shoot it (apple, for example). What does that make you think of? (Hunger, perhaps. So you eat the apple and shoot the core). What does that core make you think of? (Garbage, perhaps). Shoot that..... do this for the entire roll.
(Disclaimer-- not my idea... this is the idea of the photo teacher I am substituting for--but I think its brilliant!)