The two most powerful pieces of advice I got were from teachers at Columbia. The first was to write with the urgency as if it will keep the wolf at the door at bay. The second was to leave "fun" to the Tom Clancy's of the world. I followed the first and fled from the second.
There are only two types of books in this world. The one the teacher's teaching, and the one they're taking away from the kid at the back of the class. I want to be that second book.