Well 1 important question, do you know each units's role. As in what does Stug 3 does, what does MG do, or what does Grenadiers do.
Cause when new player comes in with little knowledge, they usually blob their troops together with mg and infantry together, which is a very very bad way to play. Identify each of the basic unit role is important so that you'll be able to learn what counters what on the field from the early game to late game
TL;DR: I think I know the basics of unit roles.
Well that's the way I do it in Ostheer:
I assume the StuG is in role of counter against enemy light vehicles like T70 or M3s and medium tanks. I don't produce StuG generally. Instead, if seriously needed in early I put up an Sd. Kfz. 222 and later on I look up for Panzer IV with MG upgrade.
That's kinda the way my friend wanted me to do. Then I might have played a bit on it.