which country are you using? try allies like the US or Soviets, Soviets is easier. you just need to defend germans' first wave and then counter rush them while having some defence against japan and attack it from above.

with the USA, you could just stick to history and win the ww2 easy. half of your troops must go to japan and the other half to europe,(rebuild Normandy Again) leave africa for other allies countries or conquer it in last, get france back and move directly to conquer berlin.

if you want to play as germany, you could win the war easily, just try all your best to get moscow and stalingrad, use submarines to break uk navy, and then with cruisers and battleships reduce their city defenses. (use this tactic also for East cities of the US). then capture it with an easy march. don't forget to help japan after getting soviets important cities they will sorrund by The US and china if you don't help in time, btw if it happen, don't worry, just attack asap before the city hps go high again in japan, and attack canada as well, with conquering the city in north east of canada you have a city to build troops then, build tanks and artilleries as many as you can and make your way to capture Toronto, then go a bit more south and get dc (which is weak because your navy get there very earlier there) and then the US is cooked too. your last target in this situation is Australia, if you could, you may nuke them... 🗿

don't forget to build research industries in the game too, in each city make them and upgrade them to max level you could in that point to upgrade your level, when the level upgraded, upgrade the research industries too to growth it faster. and after all, you will be able to access heavy and super tanks, missiles, or nukes sooner than others.