I wrote in an earlier post that balancing strength and speed was important in training. Keeping all three dimensions in mind is the other.
Quickness (Width) - changing the direction of your momentum on a dime
Speed (Length) - accelerating in one direction
Jump (Height) - playing above the crowd
Almost all professional players have all three of these, so it can be hard to distinguish the difference sometimes. Here are some clues to help you figure out where you may be naturally gifted, and where you need to spend extra time in the gym:
Players with great speed usually thrive in "vertical" situations, particularly the fast break. They also can be adept at driving to the hoop, using speed to blow by defenders.
Quick players use a flurry of stops, starts, and sideways shuffles to embarrass defenders. They are also great perimeter defenders (when they put their mind to it) - they can shuffle back and forth unbelievably fast.