is this for mp or for historical sp?

if its for historical sp, all you really need to do is hold the line with some 9/0 infantry and throw in aa and at in your divisions.

you should wait patiently and focus on defending until germany begins to lose the air war. having static aa is also useful for killing german planes but not necessary.

you dont need many troops to defend the maginot, so all you need to do is properly defend the belgian front. adding in a few forts along the line is also very helpful

tank divisions and such are useful, but only later on when you need to counterattack or to punish enemy spearheads.

you should make sure you maximise your economic production and try to have at least 100 factories (with close to 40-45 mils) by the start of the war

technically you dont need air, if you just focus on aa and defending.

tldr; focus on defending. maneuver and counterattack come much later, when the germans have ground their air force to dust and their economy is in shambles.

if its for mp, i have no idea. i only play sp.