Go find a back-of-the-book blurb of a published novel that you haven't read yourself (if you can't find one, just go look at any book listing on Amazon), then spend ten minutes writing as if you wrote the book yourself.

Note: It doesn't have to be the beginning of the novel. It could be a scene in the middle, where anything is happening. This is meant to be just, take someone else's book blurb and see what you can make of it.