Back when I first started this blog, I did a few posts on the idea of my Fantasy Manifesto-- a series of guidelines of what I wanted to avoid in writing fantasy. Looking back, there's elements that I still agree with, and elements that I don't.
1. No Fucking Elves. The principle behind this, I still hold. The presence of elves tends to indicate lazy worldbuilding, which then tends to lead to uninspired writing. I think there could be a good elf-using story out there, since the concept of what "elves" are in folklore is actually a lot wider than their typical fantasy usage. But I mostly see elves used as a sort of culture-building shortcut.
2. Don't Rename the Wheel. Again, I'm still behind this idea: if a perfectly good word exists, don't make up a new one. I recently read something for critique that did the inverse: using a perfectly good existing word, and have it mean something utterly different (in this case, the author created a unique creature and called it a horse). That said, I'm all behind creating new slang that exists in a world. Slang is constantly evolving, and the way people say something can change from year to year. Well done slang, of course, is when the reader can quickly pick up the meaning and follow along.
3. No More Chosen One. There can be interesting twists on this cliché, of course. One thing that always struck me about this cliché is this: if someone is chosen, then who is doing the choosing? And what gives them the authority to do that? I don't know of a story that explores that very much. Harry Pottter did a good job of showing the burden Dumbledore took upon himself in mentoring Harry, but ultimately he wasn't the one who chose Harry.
4. Dont' Copy and Paste Cultures. I still believe this is crucial, and I still believe it is very hard NOT to do, to some degree. What fascinates me is how many times I've seen readers complain about something not being a straight copy of medieval Western Europe. Though I have to admit something of a bias: it used to be that a copy-and-paste of something European will always bother me less than a copy-and-paste of Middle Eastern or Asian. I'm starting to get over that. I think Amanda Downum did a very good job creating an Asian-based culture in The Drowning City (though it helped she drew more from Southeast Asia than China or Japan), and I am looking forward to seeing what she does in Kingdoms of Dust.