I'm a salesman. Pleased to meetcha.by Dave Butler
So the first page -- the first chapter, the first part, but especially the first page -- is a prospectus, a sales brochure, for the rest of your book. You need to make the first part of your book great to read, and not just in any old way; whatever it is that makes your book as a whole great (romance, excitement, fine prose, witty dialog) should be here in spades. If your novel is a romance, show your protagonist's broken heart. If it's a comedy, get in as many of your best licks as you can. If it's a gritty P.I. novel, your protagonist needs to get punched in the face on the first page.
George Lucas did a great job of this in Star Wars: Episode IV. What do we open on? Spaceships shooting each other. We don't know who the story is about, but we know it's going to be full of awesome space opera action. George Lucas then did an abysmal job of the same thing in Star Wars: Episode I. What do we open on now? Uh, a trade mission... something... something. Boring. What's the movie going to be about? Something... something. Boring.