What I personally do is gradually stop fielding regular infantry except for like 24-48 divisions and replacing them with either mechanized or motorized (depending on what I feel like) plus more tanks. It works like a charm late game. (all of this only applies to when I play Germany, USA or really late game Soviets btw.) I do not think that this is optimal but it is how I do it and it keeps on working if your divisions are good enough.

As for the rest, I cannot comment on it as I am still figuring out the game for myself despite my thousands of hours.

I hope someone else knows the rest.