Add the Element of Surprise
If the reader can tell you what is going to happen in your story by reading the first few pages of your book, then why should he read on? If everything that happens in your book is predictable, a reader, be it an editor or agent, will grow bored. Shake things up by adding the unexpected.
If, when doing your reads, you discover your book is predictable, look at all your plot points and make a list of ten different things that could happen. The first three may be as predictable as the one you've already written, the last three may be too farfetched, but study those in between. You may find a new twist to give your plot just the excitement it needs.
Look for those mundane conversations that lack sparkle. How can you add some bling? Can you make a suspenseful scene more suspenseful through dialogue, a humorous scene funnier, or a sexy scene sexier? See the following example:
Use dialogue to make your characters jump off the page and come to life for your readers.
Your characters react to everything that happens to them in the course of the book. While to some degree, they should respond to the situation “in character,” it's wise to remember that in tense situations (which should happen frequently in your book), it is human nature for people to occasionally react and make choices that might seem shocking to others and sometimes even to themselves.
Creating characters means you motivate your characters to react in certain ways in different situations. However, as it is with real life, your characters should sometimes do the unexpected. Having your characters make surprising choices that still fall into the realm of their characterization while raising a reader's eyebrows is one way to keep your reader reading and enjoying your book.
When doing your last polish of your book, look for character responses to stressful situations. Have you taken full advantage of your character's reactions? Do their responses sometimes give the reader an unexpected surprise or insight into their characters?