Be a ball shark. A ball counter.
Yes - just like cards - tennis is a game of finding patterns to have the winning formula!
Every time your opponent misses - make a mental note of whether you gave them a forehand or backhand? A sliced ball or top spin? A deep ball, approach or short? A volley or overhead? You see - EVERYONE has weaknesses. Look for them. Play to them! And also - do the same for when they hit winners! Stop giving them their favorite balls!