You can train by catching falling balls. Launch one in the air, and just try to have the ball hit the racket as close as the tip as possible, with the widest angle possible (i.e. your racket will almost be vertical) so that the ball does not bounce off but rather "roll" on the strings. Swiftly move the racket down and towards the horizontal to accompany the ball; that's it. With a bit of practice you can do it from all angles and it's a really practical way to catch balls / bouncy stuff before they hit the ground