E.E. Knight, author of Way of the Wolf and Valentine's Resolve, has posted 20 no-no's for science fiction and fantasy writers on his livejournal.
1. Head-hopping: I'm a fundamentalist bible-thumper when it comes to picking a point of view for a scene or a chapter and sticking to it. So many people send me stuff that seems to be in one character's point-of-view, then another character will have a brief thought about the first character, then we go right back to the first. [Sidebar: Dragon Strike will mark the first time since the Lara Croft media novel that I've written from more than one POV in a novel (I don't count my little VE scene setters or the opening paragraphs of Thunderbolt)]That, or it's written in a nebulous 3rd person omniscient that flirts with locking down into a POV but never quite gets there. Boy is that frustrating. Let me feel, hear, smell, and taste what your characters are experiencing, please! Sensory detail is one of the best ways to draw a reader into the world.
2. Logorrhea: Having something between two and a dozen words pull the weight of one. I can't tell you how often I read stuff like "Thinking back on her past, she remembered her childhood of twenty years ago, when as a six-year-old..."