Principle one: Re-take Germany, but still protect Southern Europe.
Principle two: Do whatever you can to disrupt Soviet momentum. The key in war is to get the enemy to react to you, instead of you reacting to the enemy. Such a task is not easy, seeing as how the U.S.S.R. starts the game with more offensive material.
Principle three: Germany is a very important part of this
war, so it will change hands often. That's unavoidable. You want to buy
a balance of aircraft/tanks/infantry to defend your territory, but still
have the offensive punch to push ahead into the Eastern Block if the opportunity
presents itself.