At Writing For Charity, the writers conference I mentioned a couple of months ago, I spoke to Jeff "The Genius" Savage (my nickname for him, not his) and he gave me some great advice that I've thought of many times since he spoke it. You know when advice crosses your mind repeatedly that it has to be great!
He talked about setting a scene in your writing. We start zoomed way out, surveying the setting, catching a few glimpses of the world we're in, what life is like. Then the camera zooms in and we catch a few specifics, and as the camera narrows in more, we get to the point of the scene and that is our focus.
Something I have a tendency to do is once I get to the focus of the scene, I can inadvertently veer away. In analyzing several scenes I've written, I've found that this is a common problem for me. Right when you get to the good stuff, you don't want to diverge to a less important conversation, or wax poetic about the color of the sky. Imagining the scene as a camera lens slowly focusing in really helps me to stay the course.
Great advice from a great writer. Hope it helps!