Here is an idea for developing great ball tracking, quick reaction and feel…
As a coach, I sometimes carry with me a basket containing a mixed type of balls: some bouncy (new or old), some “dead” (that lost their inside air), some “spongy” (the over-sized sponge ones for little kids), etc. This basket I take out on the court when I want to work with my students on quick reaction, footwork and feel.
(Basket Tennis Drills)
I feed those mixed balls to my student and challenge her to hit them all over the net. The benefits of this drill is that I make the player get out of her comfort zone by not having to deal with the same bounce and speed of the ball all the time. She also develops quick first step reaction by having to adjust quickly to the bounce and depth of the different type of balls.
If you are a coach or parent of a tennis player try doing this drill sometimes but make sure he/she warms-up very well before the drill begins.