There. Read it? Good. It's great, right? It's simultaneously obvious (of course you don't want to be predictable!) but extremely informative and helpful. Do You Start One Story But Finish Another is my favorite section. It cuts through all the crap and gets to the heart of today's topic--beginning in the right place. Sometimes it's difficult to find the start of your story. Most likely, you're starting too soon (and if you're tacking on a prologue you're probably starting years and years too soon). It's critical to begin the story in the proper place for two reasons. First, pacing. Somewhere in your mind, whether you're a pantser or a plotter, you have to be aware of the pacing of the story. Starting in the wrong place can throw off your pacing and ruin the rhythm of the entire story. The second reason is audience. You need to grab the reader by the throat, the heart, or the balls, and never let go.
You have to be quick to grab a reader. They're slippery, fickle things. They want you to grab them, but they're not going to make it easy for you. They want to be seduced into your story, but they'll play hard to get and search for any little errors, pet peeves, or bugaboos to use as an excuse. If you lose the reader in the first page, chances are good you've lost that person forever. Even if the rest of the novel is totally their cup of tea, they'll never know. Maybe one day a friend will convince them that they should really, really try your book, but you don't want to take your chances on that, right?
Learn to phrase your story question is larger terms, so that you can provide a twist in the middle and still keep telling the same story.
If you're writing a romance, you need to know if you're starting along these lines: "Can these two people fall in love?" "Can these two people stay in love?" "Can these two people defeat the antagonist and stay alive (while falling in love)" etc. Change the questions depending on your genre and purpose, find the answer, and start at the beginning of that answer. If the point of the story is Character A and Character B falling in love, Character A and Character B better meet right away. I promise you, nobody is interested in the mundane details and regular routine of Character A's life. You may write it, but be aware you're doing it for your own sake and not for the reader's. Take it out on revision and start the story at the actual beginning--when the two characters meet. Or in the case of a mystery, when somebody dies or something is stolen. Or if it's a thriller, when the bomb under the table starts ticking down.
It may take a handful of attempts to find the true beginning. Don't stop searching for it. It could make all the difference.