This is a series of articles I recently wrote and posted in the STRATEGY forum. Rather than producing them all here again, I decided to simply post the links to them, which allows you to see the useful comments of others.
1. The Early Game.
2. Know Yourself, Know Your Enemy.
3. Using Diplomacy.
4. Essential Targets.
5. Keep your Focus.
6. The Stab.
7. Avoiding a Stab.
8. Bringing it Home.
9. Avoiding the Stalemate.
Addendum: A Note on Etiquette