Just takes some practise. Pretend the button side of the controller is the face of the racquet... so for forehand top spin, just hold it like a real racquet (buttons kinda facing down) and hit at an angle, or twist in the topspin direction after you've hit the ball... it'll still do a late top spin. For backhand, hold the controller with buttons facing down and swing sideways. If that doesn't work, give it a twist as you hit the ball.
Tennis is great fun, but i'm finding it too easy now... at about 2100, so barely getting points for winning, lol.