DO Make it unique to your voice and style. The opening pages will be your first impression on the reader, agent or publisher. Make them shine. It shouldn't outshine the rest of your story though, it should be one of those matches made in heaven. Have you ever read a book where the opening pages hooked you, but it didn't fulfill the promise? If so, you know how important it is that the promises you make in the opening pages bear out for the remainder.
DO Fit your opening to your genre and audience. If you're writing a romance, there needs to be a hint of the hero and heroine at the outset, where they are in life and what's going to bring them together. Depending on your story they may meet in the first page but definitely by the first chapter or two. If you're writing a mystery, you most likely want to pose the question or mysterious event early on. You may have the next Joe Friday, but if you spend the first pages just describing him without including the mystery, you risk losing your audience.
DO Use dialogue openings sparingly. This one is sometimes a pet peeve for agents and editors, but it depends on the story. As with most rules, it can be broken for effect. If you do choose to break this one and open your story with dialogue, be sure it sings, and identify your speakers. Opening a book when you don't have any idea who the characters are and why they're saying what they're saying can annoy readers. See more about dialogue below under 4/22/11 post.
DON'T Be cliché. Starting with a character waking up may not get your reader to open their eyes to your great story.
DON'T Start with a lot of description. While you need and want to give the flavor of your setting, opening paragraphs of lush description often aren't dynamic enough to capture the reader, unless you do it exceptionally well. Often it can be weaved into the narrative as you open the action of your story. The inciting incident (more on that later).
Some last thoughts:
Whatever you choose to open with, be sure you make it sparkle.
Questions or Comments on this please leave a comment or email me at firstname.lastname@example.org