Many beginning players (and some who are more advanced) focus so intently on meeting the ball with the racket that they make only stiff, short strokes or blocks. Given how quickly balls can move, this concern can be understandable to avoid missing entirely.
However, short, stiff strokes are limited and can never create the power and spin of longer, freer swings. To develop longer strokes, try consciously extending your backswings and follow-throughs a little bit at a time in practice rallies. After a while, you will realize that you can pull away from the ball without fear that it will be gone when your racket returns to the striking point.
In lengthening your strokes, also remember that a table tennis backswing should start fairly late as the ball approaches, and lead back into an immediate forward swing without any pause. Unlike tennis, you don’t want to bring your racket back too early.