The flight director is a useful tool, but know when to follow it, and when to "fly through" it. Remember that the airplane is not the master and you the slave; it's the other way around.
Have you ever had a bad command from the flight director? Ever had one give you a sudden fly-down indication during an approach, or something else that you knew wasn't right, given the data you had before you and your own situational awareness?
The first rule always applies: fly the airplane. Use the flight director, but don't let it think for you. Remember that it's supposed to enhance your awareness, not be your brain. It's there to help you, not control you.