My key to tactics is adapting my approach to meet the enemy. There is no one size fits all strategy, so being able to replace lost units with the correct units at a rapid pace can make the difference in surviving or not.
The first rule of tactics: Find the enemy, don't let the enemy find you.
You need to know what the enemy has and where. Either scout with planes, or submarines, or use spies to get a picture of what you are facing.

The second rule of tactics: Plan for a 4 to 1 advantage in direct attacks.
So if I am attacking 2 units, I want 8 units. More is better to a point of course, but by having 8 units in my stack I do more potential damage, and the defensive damage that the enemy does will be divided among all 8 units. Of course consider the effects of terrain on your units.

The third rule of tactics: Let artillery do the work
Artillery will kill the enemy from a distance, so you don't lose units in the process. Artillery are also fragile, so they need to be protected. At this point in the war the enemy doesn't have any airbases in range, so I don't have to worry about bombers, so I will put a heavy force between the enemy and my artillery, and just let them bombard, and then move on to the next target.

So instead of blundering in with my tanks I just have some patience and let the artillery do their job. Of course you need quite a bunch of artillery. One or two don't do a lot.
The Fourth rule of Tactics: Shock and Awe
Use speed units to grab undefended provinces. This cuts the enemy territory down, which gives them less places to hide, and gives you more places to hide. It will make your advance faster later. Even if you have to retreat to preserve your units and let them recapture that territory again you have delayed, disrupted, and demoralized the enemy. Some parts of war are psychological as well, so when you take territory even if it was meaningless some enemies may just give up without fighting back. If they do fight back they won't know if they should try to take back the territory that you just stole from them, or maneuver around you and try to run amok behind your lines.

I like to do shock and awe on a large scale when I get a good spy report and have an enemy that isn't paying attention. Racing around behind their lines if I can find a good opening.
The fifth rule of tactics: Don't forget your air support.
While Anti Air units in high numbers are an important part of a balanced stack I also use my own planes to defend my fragile forces. Interceptors on patrol over my units will do considerable damage to enemy bombers. I get nervous if I can't provide air cover for my units.

Of course having bombers of my own is important as well, but that is a more advanced lesson 









