Theodore Sturgeon, one of the greatest SF and fantasy authors of all time, came up with a simple law years ago. The story goes that he was responding to a fan letter (or debating a lit professor) and was asked why he wrote science fiction, which is often so bad.
"Sure, ninety percent of science fiction is crud. That's because ninety percent of everything is crud," he said.
However, discerning the crud from the good stuff takes a lot of effort. Most readers must do a hasty triage when standing in the SF section of our bookstore or library. Do we take this book home and give up time and/or money for it? Or do we chuck it and re-read Ender's Game or China Mieville's last novel?
To help in this, I have come up with an informal word-list that I've been carrying around in my head for some time. I start reading the dust jacket or the back of the book, and as soon as I hit one of these words or phrases, I stop reading. In the middle of a sentence, quite often. Back the book goes onto the shelf.
Now, there are exceptions to this list. You will note that if it was applied across the board, I wouldn't be able to read J.R.R. Tolkein, C.S. Lewis, Issac Asimov and any other number of the greats of SF and fantasy. But that's part of the point. Those greats blazed trails. We should be blazing our own, not following in their well-worn footsteps almost a century later.
Here then, is an incomplete and sure to be updated list of Crud Words:
Bold new interpretation of the Arthurian myth!
Quest (especially if the quest is foretold in an Ancient Prophecy, written in Ancient Runes)
Dark sorcerer threatens the land of...
Prophesied saviour of the land/his people/fluffy bunnies
...an artificial intelligence, now out of control!
...experiment in genetic engineering, out of control!
That's all I can think of for now, although I'd note that the same rule applies to covers. If there's a tough, cyberpunkish looking mercenary type holding a big gun or a dragon with a guy on his back, there's a good chance it's crud.