Simple answer - Practice makes perfect.

Personally, I just did a run through and rushed heavy fighters and strat. bombers. Very un-meta, but it was fun to RP a heavy air liberal confederacy.

Went down Superior Firepower and stuck to 7-2s, basic but effective

Ally the entente, grab yourself a couple 24 stacks of those troops and play a war of attrition. Make an encirclement every now and again and try to nab the east coast. With time, the US will lose more and more equipment until you can plow right through them.

just build 40 width medium tanks

Divisions: 3 armies of 7-2 Infantry, 1 army of 12 14-4 Marines & 12 14-4 infantry, 7 divisions of 40 width Heavy Tank, 5 divisions of 14-4 motorized, 24 20-width garrisons with engineer, finally take control of Mexico's divisions (about 21) to defend Arizona

Doctrines: Mobile Warfare - mobile infantry branch and Volkssturm branch (for extra manpower) & Battlefield Support

Diplomacy: doesn't matter. I went Golden Circle cuz it seemed more interesting. Right now Entente will always die to Germany so it's probably not a good idea to ally with them

Navy: build DD 2 with sonar 2 and depth charge 2; get convoy escort doctrines and escort in the Caribbean; block off all North Atlantic sea tiles & Gulf of Mexico

Attack plan: seize the US east coast and Pennsylvania, that'll give you the bulk of USA's factories and steel so after that the fighting will be very easy. Don't bother fighting their navy, just escort and set ~400 tac bombers on naval strike.

You have to build a lot of civs at the start, and this mod makes combat feel different since it starts in 1942 usually, which is when defenses are hard