Here's another casting tip from Andy Mill, one of the most decorated tournament fly fishers in the world.
He suggests that the basis of a great fly cast is the ability to accelerate the rod, and then make it stop abruptly. Doing so creates the force you need to form tight loops--much like the force you create when you draw back on a bow and release the string.
Start by practicing at a short distance, with the rod parallel with the ground. You'll be able to not only see, but also feel, the starts and stops as they happen, as well as to good casting loops they form.
With practice, lift that same stroke above your head, and fire at the target. If ever you find your cast getting "mushy," odds are, that's because you're not accelerating and stopping the rod precisely.