To effectively return a serve with a lot of sidespin, position yourself early and anticipate the direction of the ball based on the server's movements and body language. As the ball approaches, adjust your stance to align your racket with the trajectory while keeping a firm grip. Use a combination of a stable base and a slight forward lean to counteract the spin, and aim to make contact with the ball at the highest point possible, ideally around waist height. Focus on adding your own topspin to the return by brushing up on the ball, which helps neutralize the sidespin and enhances control. Follow through in the direction you want the ball to go to ensure accuracy and balance in your shot.