I seem to be having a little trouble getting my plot up off the ground. I have a good of the Beginning and the End, but I'm having trouble coming up with a Middle. I'm having trouble worldbuilding, too - I don't know how to get started, where to make my characters exist. A have a few good storylines in mind, but I need to make this world live and breathe, have real, believable characters in it. Any tips on getting my imagination going?