There aren't any real strategy guides. You learn it as you go, really.
So let me tell you what I've learned. If possible, you should lock yourself into a corner of the map - ie one of the poles. This removes one front which you can be attacked on, but opens you up to several new enemies. Many powers tend to get locked up because they consolidate their continent too late, or focus on building too many armies early. To be truly successful, build solid alliances within your continent, and establish yourself on another one. Once you're in a solid position on the second continent, you can proceed to consolidate your home continent one. Other players wait too long and then try to breach another continent which is controlled by a single player. And finally, fleets are important. Waaay more important than armies, since sea spaces are a lot more valuable than land spaces. One fleet in EAO can threaten 8 or so territories on Africa, meaning whatever power you're trying to invade needs 4 units to cover it at least. But, if you moved too late and EAO was protected, you're stuck, and its very easy to get stuck in the late game.