Right?! Super hard
I think the best thing I ever did I stop needing all my units to survive. You are gonna lose troops, and lots of them, and that's OK. There are more!
Super duper tip: the mouse-cursor turns blue wherever there is cover (forests, hedges), making units in there harder to spot. Always put troops in blue spots or towns unless making a big push.
Here's a few generic tips that I feel are a good enough baseline strategy for defending (which is what you want to be focusing on at first probably).
Recon is super important. Every front should have 1 or 2, with Very Good optics eye-sights. You get Excellent optics on choppers, but they are more vulnerable. Use relatively cheap recon so you can deploy more.
This comes down to see'em first, shoot'em first. Optics on non-recon units can be pretty crap, so if you want them to engage at range, you need recon.
Put fair amounts cheap regular infantry (10, 15 strength per unit) inside buildings at strategically relevant locations. In buildings behind them, have AA infantry (get the best, with 70% hit chance if you have them). On the buildings on the edge of town, put ATGM infantry if you have it, or the longest range AT inf you can find.
This makes it so enemy vehicles get destroyed on approach, any planes coming to bomb getting attacked, and any vehicles that actually enter town or get too close get attacked by tons of effective close-ranged AT.
Put a couple of tanks behind infantry, in cover, with line of sight and range to incoming roads.
This isn't always possible, but ensures that any lighter vehicles, usually bringing in reinforcements or supplies, get taken out as far as possible. Infantry walking out in the open is as good as dead!
Behind tanks, consider having ATGM vehicles (anti-tank guided missile, GUID in weapon descriptions).
ATGM vehicles tend to have little to no armour, so they'll go down at the first hit. Tanks with stronger armour will take the brunt of enemy fire and survive for longer, while your longer ranged ATGMs take enemies out from safety
On more open areas, focus on using tanks and ATGM in forests/hedges. Keep your ATGM vehicles separated from each other, because an AoE weapon will take them all out.
Where your support and command units are going to be, have strong AA consisting of more than infantry. Turn off radar on their weapons until enemy planes show up and are in range, or they'll get destroyed.
During defensive battles, just keep shoring up your defences as you lose units. Try to keep an eye on AT ammo and get some supply in before you need it (guarantee that's going to be during the next major offensive). React to what the enemy is doing... if they're bringing in lots of cheapo tanks or vehicles, maybe get a few extra tanks/ATGM in, or some spam arty on their approach. If they're getting heavy tanks tanks in, get some of your own, or long-ranged air-based ground attack.
Also, just watch some youtube battles, and realise how little micro the pros are doing all the time. They only do it when it's necessary, or to set up the troops. Then they are mostly on their own!
Final tip is, after you've tried a couple of battles, just build your own deck for fun. It's what allowed me to truly understand all the different unit types and how they might fit together. You don't even need to use it - feel free to go back to SP afterwards. It just really helps get a feel for the units
Hope this helps!