Always tell us where we are. And don't just tell us where something is, make it pay off. Use description of landscape to help you establish the emotional tone of the scene. Keep notes of how other authors establish mood and foreshadow events by describing the world around the character. Look at the openings of Fitzgerald stories, and Graham Greene, they're great at this.
What is a scene? a) A scene starts and ends in one place at one time (the Aristotelian unities of time and place-this stuff goes waaaayyyy back). b) A scene starts in one place emotionally and ends in another place emotionally. Starts angry, ends embarrassed. Starts lovestruck, ends disgusted. c) Something happens in a scene, whereby the character cannot go back to the way things were before. Make sure to finish a scene before you go on to the next. Make something happen.
I usually start with something that has some energy, like a compressed character or a situation that's wound up like a spring. Then all I have to do is let it go, let its energy carry the story. And that may not turn out to be the beginning of the book.
