Armor isn't as strong as you think, take advantage of boccages. It's very important to realize and pay attention to the fact these lines of trees which give you a green shield (the highest level of cover) cannot be traversed by armor/vehicles, only infantry and artillery!

-A few squads of infantry, an Mg, an AT gun can turn into boccage into a nearly impenetrable defensive line.

-Not only can vehicles not drive through boccages, they cannot see OR shoot through them.

This game is all about pressuring the enemy with a constant presence of units on front.

-Like I said in step 1, those boccages of trees are like a unassailable wall if they are manned properly. However, keep in mind there are openings (roads, etc) that pass between boccages. I often like to keep a tank behind my boccage, with its cannon pointed at this opening. This creates a kill-zone, should the enemy try to pass through it.

Armor is extremely slow, even on paved roads. This means big armored pushes are almost impossible. Whenever pushing, take a single boccage at a time, using leapfrog tactics. Set up your tanks on your side of an open field, covering your infantry/artillery/AT as they cross the field to set up in the next closest boccage.

Another key thing to keep in mind is that you can't call in reinforcements WHEN you need them. To clarify, SDN44 is a lot like a game of chess. You need to guess what you will need AHEAD of when you actually need it, because units will never arrive on time.

It can be very tempting late game to forget about recon, but you should force yourself to constantly check if a group of units has at least one recon unit with them.

-AA isn't designed to kill planes outright. It's designed to scare the ♥♥♥♥ out of the pilot and make him run away before he can do any damage to your units.

-Don't try to zerg rush the enemy's main concentration of strength with multiple bombers. That is where they will have the greatest concentration of AA. You will lose more points than you will inflict.

-You are better off spending your points on artillery and bombing the ♥♥♥♥ out of their main focus of strength.

-Planes are best used where the enemy is WEAKEST. My theory is that planes are best used for killing enemy reinforcements. In the late-game, send your planes deep behind enemy lines, where their AA will be the least concentrated. You will occasionally get lucky and kill one of their fancy and expensive tanks as it is first entering the map.

Hope this was helpful.