You have to follow history atleast slightly. Pull all russia forces back to your cities and if that wont hold think of puting every man in moscow. That is an incredible amount of defense. It is also key that america and the UK take the sea and put pressure on Germany so they cant devote all their forces and money to killing russia. They might even want to consider shiping planes over that russia can take control of. 8 planes in moscow with a role of 4 or less is incredible defense against tanks. If the Germans are going after russia full force just pull back to moscow and let US and UK take the covoys back, supply troops, and put pressure on Germany. If Germany always wins it is because the people playing US and UK suck at the game.