I love learning something new and by chance I happened (on EE) to discover the shoulder-in entwickeln exercise of Walter Zettl today. You can read all about it here http://www.walterzettl.net/pages/exercise.html and it's a great one to have in the tool kit. I tried it in walk and trot today and it really does open out the shoulder and help the balance. I tried it in conjunction with another shoulder-in exercise I use; shoulder-in down centre line, straighten half pass (same inside bend) straighten shoulder-in opposite rein, straighten, half pass and so on.
Can't wait to ride tomorrow and play some more.