The key to playing aggressive tennis is to always be moving. If you stand still, you won’t have time to get moving, before the ball comes. You’ll be late and you’ll have no choice but to block it back and hope your opponent makes a mistake.
If the goes into the net, you need to get lower. If you’re above the ball, you’ll always be hitting down on it.
If the balls goes long, you probably didn’t finish your swing. Move forward through the ball to drive the ball.
The best way to keep yourself moving is to start out of position so you have to move to get into position. This tricks your mind into keeping your body moving, vs trying to be in the “right” place just waiting.