big topspin forehand?
like other posters said - hit the ball on the rise, take away your opponents time to load up & recover - start there, and then, decide if you also have the ability to add in movement to your shot. I think taking it on the rise and putting it back deep is your best tactic. If you can also move that shot around its only a plus.
Next - be mindful of your chances. If you know the player hits consistently, with deep topspin, if & when you get an opening, I suggest going for it and go on the offensive quick. Take your chances and recognize an opportunity to jump on them. This will be your window to win.