Honestly, it would be more fun for you to spend some of your winter time reading books about dressage. YOu will need to learn the terms that this instructor will be using, and you will want to study some of the philosophy of classical dressage. The more you read, the more quesstions you will have and the better student you will become.
As for riding the horse, I dont' know exactly what you mean by headset, but you can work on developing as good a following hand as possible, maintaining a soft but constant contact. You can work on learning to let your leg hang down, so maybe ride w/o stirrups and with a long, relaxed leg.
Really, just enjoy the winter, watch some videos and read books. There are so many good books on dressage.