Ok, first, you must level up your troop production buildings so the troops production time is really cut down.
For example
Producing a level 3 armored car in a level 1 tank plant takes 21 hours
But building it in a level 3 tank plant takes 5 hours 15 minutes
leave 4* speed maps alone until you master the game, I am decent and they are very hard.
Always build only 1 type of PRODUCTION building per city, to save resources.
Don't research everything, only what you intend to mass produce

