A large part of the game depends on who the Allies decide to attack. They can decide between KGF (kill Germany first) or KJF (kill Japan first).
For people who are new to the game, I think a KGF would be easier to pull off. All the Allied capitals are near(er) to Berlin, so the logistics are easier. Also, Germany can threaten Moscow quicker than Japan if not threatened.
However, a KJF can work against players who are used to playing against KGF. It is usually best to go this route if Japan has a bad first turn, although I have won games where I had a KJF in mind before the game started. In this strat, your goal is to reduce Japan down to Tokyo and maybe a couple other territories, and to wipe out their navy. In this way, only a minimal Allied force is needed to contain them, and all attention can shift to Germany.
Note that I don’t mean to ignore the other axis power that you aren’t focused on. This is usually only a problem in KGF, and Japan can reach Moscow quickly if left unchecked. Usually the U.S. will deal with Japan a bit in KGF, and Russia will hold off Germany with a little U.K. support in a KJF.
As the Axis, you must identify if your oppenent is playing a KGF or KJF. The nation that is the focus of the Allied attacks must play defensively while the other nation kills Russia.