I've heard many turners say "Let's chuck up this piece of wood and see what is inside."
But to end up with something that is pleasing to the eye, one has to start with some idea as to the proportions for the finished project. I've heard some that say that the widest section should be 2/3 the distance from the bottom to the top and the base should be 1/3 the diameter of the largest diameter.
So what proportions do you keep in the back of your mind when you start a turning?