Tim Pratt, in his journalscape site, ask: "Do y'all have things you hate seeing in books, that you'll sure as hell never put in your own books?"

This is easy: dream sequences that bear on the plot. Unless an engine of the plot is the manipulation of dreams. Which should be avoided anyway. Dreams in real life are not the roadsigns of our woes.

Also celebrity shorthand. By which I mean giving a character celebrity traits or physical attributes, so that the author isn't required to actually, y'know, come up with an original description.