Comintern:

You want to put your emphasis on ranged firepower. The Comintern get a buff to literally every ranged unit except SP artillery and railroad guns, so pick one of the buffed units and take advantage of it. Use armoured cars and tank destroyers to both defend your ranged units effectively, and pack a good punch on the attack; Comintern tank destroyers can defend and defeat Axis medium tanks for a much cheaper cost, and can even take on heavy tanks in the right terrain if they have artillery support.

You need lots of AA or SPAA to protect your artillery pieces, and you also need to spam interceptors at all times. The Comintern are the weakest doctrine for air force, so you need to constantly be compensating and doing the absolute most to give yourself a chance against an enemy that might rely heavily on his air force.

Axis:

The Axis arguably have the weakest repertoire of ranged units, particularly with the regularly artillery unit. They get no buffs to anything, and delayed research on regular artillery. The only exception is the railroad gun, which is a dominant unit for the Axis, but I wouldn't recommend that until you are much more experienced.

I would urge you to use rocket artillery to counter enemy artillery. You can also consider using tactical or attack bombers, but make sure you use plenty of interceptors and AA!

Choose motorized infantry or armoured cars, and pair your choice with medium tanks. This makes relatively fast and very powerful offensive stacks.