I've written a lot about things to do when writing, but I haven't spent much time discussing writing taboos. As a reader/reviewer there are many things authors do to make me cringe (not in a good way) or worse, put the book down all together. You don't want any reader to put your book down, so here are a few things to avoid:
Coincidences. In life, there are plenty of coincidences. You run into an old high school buddy on the street, you decide to drive to work instead of taking the train and your car breaks down, etc. Coincidences don't have a place in novels. Your protagonist cannot happen to find a gun in a dumpster. Your villain's car cannot break down just as the police are on his tail. One or two coincidences in a novel are okay, but you have to earn them. Make it hard for your characters, don't take the easy way out.
Head-Hopping. This is when the point of view shifts from one character to another in the middle of a scene. It's jarring and it pulls readers out of the story. I understand that it's tempting to tell the story from all perspectives, but if you need to shift point of views, insert a section break before you do. But even that sort of feels like a cheat. I'm more impressed with a writer who can sustain a scene and convey another characters emotions or reactions without going into their head.
Stretching Realms of Believability. Yes, fiction is made up, but you want to avoid disbelief. If you create the world of your story with enough authority, readers will follow you anywhere. Too many far fetched twists or plot lines, will increase readers disbelief and possibly turn them off to the story.
Losing Your Characters. This is particularly true for thrillers where the action drives the plot. It's easy to lose sight of your characters, for them to turn into talking heads or for them to fall off the page all together. But even in thrillers, it is the characters that breathe life into the story, and if you forget about them, your story will fall flat.
Being Predictable. When you're trying to figure out where to take your characters next, the first answer is usually the most predictable one. Be creative, avoid cliche, find a solution that readers won't expect. The best part of reading is being taken on a ride, not knowing what twists and turns will come up next. Predicting the end eliminates the joy of the journey.
Feel free to comment your own pet peeves or writing taboos. I'm sure there are things I left out!