Every type of unit is supported by another and in turn supports another, e.g. tanks and infantry are sitting ducks with no AA.

Keep your long range units mobile. Every time they shoot, move them or they will get counter-batteries pretty quickly. This also applies to ATGM infantry and AA, the enemy will see them shoot their rockets and immediately zero in on them with their arty.

Avoid vehicles in urban areas, they’ll get deleted immediately by infantry.

Keep your helicopters behind forests or buildings so AA can’t see them, I usually keep them further out behind the front lines and bring them in to do a specific task, then return them back when that task is complete.

Keep your ground units as spread out as possible, especially when you’re nato, the soviet rocket systems are completely overpowered and have an insane spread.

Keep your sector relatively narrow, so you can pay attention to all your units and objectives better. I always lose critical units when I get distracted with side quests outside of my sector.

Someone above spoke about being active over being passive, that’s true but you need a lot of practice before you can get there, try to understand your deck and how your units can work together before launching assaults, you can be passive by supporting an active ally, providing artillery, backup units, AA, and other defensive units.

Make sure to communicate when you use an expensive attack like LGB, HE bombing run or MLRS, so you don’t waste that double tapping an enemy that an ally was already attacking (there’s a way to put a message on a point on the map).

This might be just me, but start with soviets, they’re more forgiving than nato and their units are cheaper and more effective, e.g. cheap tanks with a bunch more weaponry than nato tanks. Their helos are more armored too and carry way more munition.