IMHO;
1. Field a cheap, reliable MBT. 76.2 mm gun. Don’t German it up (DGIU). No overlapping wheels. 3 man turret and sloped armor.
2. Get rid of Me-109 ASAP. 10% were lost in accidents due to narrow undercarriage. 12.7-14 ish mm guns. 20 mm if can work. 3 per side, 2 per if 20 mm. Cheap, reliable. DGIU. Drop tanks. Look at the Davis wing for longer range.
3. Rotate pilots out to train newbies.
4. A crap ton more pilots.
5. Cheap, reliable 4 engine bomber and LR Patrol plane. DGIU.
6. Have a cheap, reliable chassis for StuG III type and SP arty. DGIU.
7. Halftrack like the US. Banded track.
8. More trucks.
9. More arty of all types.
10. Some type of early RPG or better man portable AT.
11. Electronics of all types. Radar, prox fuse, radar detector, cavity magnetron.
12. Integrated Day and night air defense system.
13. Realize what you have in the jet engine.
Ramp up economy to true wartime one. 24/6. Women in workplace. Women pilots. Daycare at work.
Get rid of all the different fiefdoms. Consolidate to a few headed by the right people.
Shoot Goring.
Real assembly line manufacturing. Find the right type of each weapon and make the crap out of it. 40s version of Lean manufacturing.
Find some way to not fight a multi front war.
Like the above, see if you can make peace with GB and never fight the US.
Realize that the USSR will probably attack you one day. Stay allied as long as possible.
Don’t make the 3rd big blunder (Behind never get involved in a land war in Asia and going against a Sicilian when death is on the line) by trying to actually invade the USSR. Ask Napoleon how that works out.
Reliable oil supply.
Find some way to not be one of the most evil, twisted regimes in history and don’t systematically murder millions of people.
Like the War Games post. Don’t fight in the first place.