Although the Usual Russian Strategy of, one space back huge armies of infantry and artillery, usually is quite effective against the usual German onslaught. Perhaps the Russians should not be so predictable because it seems that though this strategy might work the first few times you are giving the German player the power to be creative with is Barbarossa.
Therefore I was thinking, assuming a G3 or G4 attack, mass 3 large armies. The biggest in Eastern Poland, the 2nd largest in Belarus and a smaller but powerful force in Karelia. This is assuming Germany has massed forces in the east and has some infantry in finland. Now the German player will be forced to divert the bulk of his forces to Eastern poland, as it would be impossible to bypass. The russian player would almost assuredly lose eastern poland but at a very high cost for the germans. Now the russians can succesfully counterattack the germans massed in Eastern poland and force the germans again to take out the large stack imposing on their front lines. As Russia do not defend Leningrad or the southern regions as they are relatively unimportant. With the Karelian infantry take finland and Norway to hopefully meet up with some brits or americans by 2 or 3 turns after war has been declared, from there Germany is doomed!