As a teacher/librarian, one of our roles is to guide our students into choosing appropriate ways of expressing themselves in the class & school setting. But when does guiding them lead to stifling their own creativity?
My first reaction was to ask the question, "Well, if you have to ask?" then maybe what you want to do/say/write/draw is not appropriate for a class assignment.
One of my student's has an assignment where they write a surreal poem. His initial expression was to write that this student's addiction to gum was analogous to an addiction to crack. Then his second choice was an addiction to cigarettes. I told him that probably was not the best analogy. Then he did something about a dog & a bone.
Still, I'm not sure I was very comfortable steering him away from his initial response only because I do feel like I'm "forcing" him to conform and poetry is more expression that convention. Not sure if it was right or wrong but a dog & bone is probably more appropriate than crack & cigarettes...