I think the key to A&A is really resource management. Since its a zero-sum game, the player that manages their resources the best will do the best, and ultimately win the game. What do I mean by Resource management:
Getting the most out of your units on offense and defense. Planes are a good example. You want to position your planes so that they can participate in an attack every turn, and provide defense until the next turn. If you position planes so that they miss a turn without being able to attack, then that’s wasted resources.
Another example is buying transports, and not having enough troops/tanks to fill them up. Again, this is generally wasted IPCs/resources.
It is vital as any country to use exactly the right amount of resources to acomplish your goals. If you use too much, then those wasted resources will cost you position elsewhere in the game. If you use too little, you will fail in your goal and again the resources are wasted.
For example, if Russia is playing to stall the Axis, then the Russian player must spend just enough IPCs on the Western front to stop Germany. All other resources go to the East to stall Japan. If the Russian player miscalculates, then either Japan or Germany will advance faster than optimally possible.
Another example, Japan must spend exactly the right amount of resources to attack Moscow/Asia, and send the remainder East into North America, or West into Europe to help Germany. If Japan stikes the right balance, then The Axis is hard to beat.
This is true for all countries. I once played the US, and I bought 3 bombers during the game, but I positioned them terribly, and they hardly ever saw combat. It was a huge waste of 45 IPCs.
The flip side to this problem of course is risk management. the closer you come to using just the right amount of resources, the higher the risk you will miscalculate, and use too few.
What do you guys think?