I read a good article on how to improve your burndown charts. It also has one of the best analogies used to describe the Burndown chart that I have read.
“As a pilot, I like to think of a burn down chart as being like the glide path of an airplane on final approach. An instrument in the cockpit tells you if are above or below the ideal glide path. If you are stabilized on the glide path (usually 3 degrees at a big airport) you will hit the runway at the designated touch down point. If you are too high, you will not make it to the runway unless you increase the rate of descent (which is not always easy to do). If you are too low, watch out for the trees!”
Well worth a read!