Hey Susan,
I would say the biggest 2 issues for this shot which cause mistakes are timing and not brushing the ball. Players do tend to rush this shot and not slightly pause before the contact which can cause the ball to go into the net a lot. Also being sure to brush up the back of the ball and try to be confident with it, so accelerating well through the ball contact.
So I would focus on good timing, as in getting the ball at the peak of the bounce or even just as its slightly starts to drop down. And using the body and legs to help which means your arm can relax a bit more and accelerate through the contact with a good brushing contact. Let us know how you get on! 🙂
