Keep in mind global is not playing both Europe and Pacific simultaneously - it is a different game.
I went for global off the bat. Played against myself, with my son at my side, a bit. Like 4 rounds, and then reset, do another 4-5 rounds, getting a grasp of the rules and basic strategies.
Grasshopper and general hand grenade on YouTube have some great videos to get you started.
I once tried to play pac alone - couldn’t get into it. Like playing baseball with one hand tied behind your back, just doesn’t work when you know what it’s like to have 2 hands.
What Germany does affects how the allies react, how they spend resources, and thus what Japan has for options and challenges. And vice versa, what the us or Russia does on one side affects what they can do on the other.
Europe is more ground, pac is more naval, and the way airpower is projected is a little different on each side due to the geographical differences. And the economy portion is Completely different between global vs one side.
And then there is tripleA. Play online. I learned more in one game against an experienced player on this site than I. 10 videos and 4 months of self play. Not just strategies, or tactics, but also how the rules interact with each other.