Russians are boring to play. You just count up the German Armor, divide them by two. Count up the Art/Inf/Mech and divide by three.
IF you have enough Infantry to sustain a round of combat without losing your 2 Ftr/Tac, you counter attack. (Meaning their hit number is equal to or lesser than the Infantry you can bring in)
If you do not, you take a step back and let the Germans move forward for free.
You do that each round - making your purchases entirely based on fodder purchases (Inf/Art/Mech) to allow your Aircraft to keep jousting in and hitting a few of the German fodder units.
Your BEST opportunity is generally the first round the Germans advance into East Poland. After that the stack gets bigger and you generally have to locate the breakoff stacks and try to chip away at those fodder units - because ALL those German units will be going into Moscow at once making it irrelevant if you’re hitting the big stack or the smaller ones. At the beginning they are likely all on one stack - making the target simpler to choose.
Sometimes the risk of an Armor or Artillery in those jousts can make a nice dent, but realize you’re likely losing them the next round to the German advance, so if trading 10 IPC of units gets 3 Infantry, you’re winning due to the lack of German fodder units once you chew them all up.