With Germany, here are some very very basic basics to follow. This method is counter to the G1 or G2 Barbarossa most experienced players are currently employing, but it is just as effective if you’re patient:
G4 German Barbarossa. Goal: spiky naval shield for Atlantic wall, armored gauntlet for Russia. Italy makes mixed purchases in support of land war in Asia (mostly land, sprinkled in air and sea). Italy can-opens territories, Germany reinforces newly taken Italian positions on Russian front. Best of all worlds - Italy gets money, Germany steps forward and can land air forces to boot. This preserves Italian forces for the next step forward.
Germany makes purchases of all fleet first round (carrier/destroyer/sub), then balanced purchases until the end of days. Never stop. Don’t let your opponent breathe. Dismantle Russia by turn 10, 11, 12 or whatever.
By balanced purchases, I mean the following - let’s say you have 60 IPCs with Germany - a fair number for the midgame. Buy a fighter, destroyer, 2 armor, an artillery, 2 mech infantry, and 6 infantry. Just keep doing it (or some variation of it… a bomber instead of a fighter, or 2 subs instead of a destroyer, or no armor and more infantry - it is adaptable to what you need turn by turn, but follows a basic pattern). Air and fleet to keep bolstering the SZ112, most everything else keeps flowing to the front. Let your imagination run wild from there. A wonderful moment will come when you realize that with Russia eventually pinned down, you can slip just a few armor and mech infantry behind the lines to go wild and take Russian economy without compromising your major force.
When you have such versatile forces - mostly infantry and mech infantry, some artillery, armor, air and sea, you are able to adapt and fight a war of both movement and attrition on all fronts. Air power can shift from Atlantic to Med to Ost Front at will. Mechanized forces can hammer away either north, south, or behind lines, at will. Infantry and artillery armies can become ground holders, and provide stepping off points for deeper excursions. They are predictable purchases… but are designed to keep the maximum level of unpredictability. Good times!