The trail arm works the same in most all shots. It lines up with the shaft of the club you are hitting at impact. Start with your putter. Set up with just your trail arm. Your wrist is parallel to the club face. Then hit puts just using your trail arm. Your forearm should line up with the shaft. It pushes the shaft through the ball. The key is that your forearm does not twist. You can then do the same thing with your lead arm. The task is to make a stroke where the arm does not rotate. Then put both hands on the putter and hit some putts. This is the same relationship of your trail arm with even your driver.