The Terrans are pretty straightforward. Your strengths are in Trade and Diplomacy (especially in Dark Avatar, with Super Diplomat), so it pays to play a somewhat pacifist game. If you stay Neutral, you can get Neutral Shipping and Neutrality Learning Centers, two very powerful technologies. Play the evil races against the good races by bribing them into war with each other, make a trade route with each race, gift an old tech to anyone who falls to Wary or lower, and coast to a peaceful victory. Unless the Drengin or Yor conquer everyone in the galaxy (in which case, you may be at risk of being steamrolled), you should be able to win reliably at any level up to Crippling or Masochistic, without any specific strategy.