Just make as much units as possible and also makes some friends (here make few people join the axis), if the soviets are fighting a war with other nation, just intervene as you can defeat soviets easily if you have 140+ divisions and soviet fighting a 2 front war, since Soviets divisions are often if not weak and inferior, you don't need more troops but more quality troops and also encircle and deplete their manpower and bomb the heck out, their supply and army will collapse and it will be easy to push them, i recommend making friends with japan (strong eastern fascist member to prevent all their troop to align in your border) and also italy (defend your lines if in case) and if possible also Turkey or Finland or both for distraction and reduce the amount of troops in your border and also recommend having medium tanks or even a lot of small tank units otherwise, it will be slightly hard to move quickly in soviet union and encircle units easily to reduce their power. Hope you benefitted. I recommend either not fighting a 2 front war with UK and France, either maintain peace for the duration or eliminate them before attacking USSR as they make or break your success on the soviets