Read my latest Hacks for Hacks column at Writer Unboxed, "The Dumbest Mistakes New Authors Make." Here's a Costco-sized free sample:
Beginning in the wrong place. A lot of newbies have perfectly good stories, but don’t start them in the right place. Where’s the right place? I recommend you begin writing in a nice coffee shop so everybody can see what a busy and creative author you are. It’s the perfect atmosphere to pen the 10,000-word prologue about your protagonist’s great-great-grandparents.
Not knowing your audience. If you want to please readers, you’ve got to do your homework. Get to know your readers by approaching strangers in bookstores. “Hey!” you’ll say in a loud, cheery voice. “I see you’re perusing the erotica section! I myself am working on an erotica novel! Can I run some ideas by you? No need to get the manager, this is market research!” When the security guards inevitably show up, pick the officers’ brains about what they look for in a police procedural.