No two shots in tennis bounce toward you at quite the same height.
One will be up around your head, another will skip low. Sometimes the ball will scarcely bounce at all.
But a key to successful ground strokes is to try to hit the ball at the same height every time. That height should be waist level.
You will have to backpedal for high bouncing balls and come up and bend with your knees for short ones.
Taking the ball waist-high time after time requires practice. A good drill is to have another player hit you balls which you try to catch at waist height. It's easier to ingrain the feeling when you don't have to worry about hitting the ball too.
Then strive to hit every ground stroke waist-high.