Originally Posted by Topspin Shot
Split step so that you're in the air when your opponent contacts the ball no matter how far you've made it in to net. So on a serve and volley, you will split well before you reach the service line. Once you land off the split, you should know where the ball is going, and then you have to move through the volley. Do not stop at contact but rather time your feet so that you land with the back foot, hit the ball, and then land with the front foot. So on a forehand volley, you want to make contact as your left foot is still steppping forward, before it comes down. Does this make sense?
I agree with the timing of the split. I don't like to focus too much on the opponent, so I developed a footwork pattern that works for me (serve, two steps, and hop). This is just a general habit, and I may vary it according to the serve/opponent. With a slow kick serve, I may be a little too early after two steps (serve still moving toward opponent) and take another step before the spilt, and with a flat serve, the return may be at my feet before I jump, so I may need to split right from the serve in no-man's land.
With a little practice, you can significant accelerate your motion out of the serve (try practicing exploding out of the serve and forward a couple of steps a couple of time when you are practicing your serve).
Regarding the footwork of the volley, I think a better mental reminder is to think about moving forward slightly during the volley because the specific footwork may vary according to the height/depth/angle of the return.