Just don’t buy tanks unless Germany preps for Operation Sealion.
You have two options in a non-lion game:
1: Mostly tons of infantry.
This can basically do nothing but hold Moscow. Germany is likely to just drive south and take the Caucasus/Volgograd/Middle East money. You’ll hold Moscow, but at what cost?
This is slightly weaker when trying to hold Moscow, but allows you to punish Germany for any mistakes, and allows you the option to push back out of your Moscow stack if Germany diverts itself southward and leaves an anemic stack outside of moscow (such as in Bryansk). A good German player will not make a mistake, but a good Russian player will force the German player to be honest and make no mistakes. Artillery let you do that.
In a sea lion game, assuming Britain/America didn’t totally drop the ball, it’s completely the opposite. You get to be the aggressor. That’s an entirely different discussion.
So, you normally can’t tell what type of game it is until G2. This means for R1, the best thing for you to do is prep for either, and what’s that? As the other two guys above me have said, and I agree: artillery. They are slow, so R1 is the only time you can build them and hope for them to push into Germany in the event of London falling, and if it’s the Barbarossa flavor this game, then they are still useful.
If/when it does come down to the Moscow fight, as the Russian player, you need to decide if it’s worthwhile to stay your ground and kill lots of Germans, or to head south and hopefully help defend Egypt to prevent an Axis win. Many Russians I’ve seen never consider the fact that you are sometimes able to just up and leave Moscow, saving all of those units to join up with the brits in the middle east.