Tips 1-5: Always play on Regent or below.
6. Build your first three cities close together and protect 'em.
7. Participate in all these forums.
8. In the late game, unload your invading forces on your enemy's mountain -- that's linked with a railroad -- and watch the AI decimate itself.
9. Always build the United Nations before anyone else, then refuse all votes.
10. Don't listen to me; read anything that SirPleb has written about winning the last GOTM.
Oh, and never throw your printer at the iMac screen when the AI gangs up in the early game.