Was re-reading this article about how much better children are at writing poetry compared to adults. I highly recommend reading it. The thesis is that once you learn how language is used, the creative ideas of how it can be used no longer occur to you. You know how to express your feelings, so you no longer use unexpected language to do so. It implies, too, that folks learning English as a second language might write better English poetry then native speakers.
The trick, then, is to be constantly practicing creativity. To teach the brain to generate the long tail of phrases. But how does one do such a thing?