The purpose of the first page is simple – to get the reader to turn the page and move on down in the book. It has to be about the story, of course, but it is even more about hooking the reader into the book and selling the book.
In my own writing the first page is not the first thing I write but the last thing. I consider my first couple of chapters as temporary, they may or may not go into the book or if they do will probably need to be rewritten after I am really familiar with the story and the characters. Then when I am through and happy with it I go back and say “Okay, now how do I get them off this page?”
Readers don’t really care about the weather or the setting until they have decided they are going to read, then we can set the scene for them. What do I like to see on a first page? An action initiated that is not completed, curiosity aroused and not satisfied, a question posed and not answered, anything that begins on the page but is not completed until the next page.
While an agent or editor may not reject a book on the basis of just a first page, most of them want the page to be compelling. They know a majority of readers standing at a book rack pull a book down and read the back cover copy and the first page. The object is to get them to turn that page and read a little further into the book, because that’s when they will carry it up to the checkout stand. And that’s why first pages are so important.