Uh, Okay. So, even my SEIV Posts weren't on topic. Here is my ultimate piece of advice.
Colonize, colonize, colonize. An empire that doesn't have at least a couple or ten colony ships on their way to colonize new planets with another ten in production is like a Zerg player without hydralisks. Oh, sorry. Didn't mean to bring up StarCraft again.
Be at peace with everyone. In tough games, 20% from the #2 player in trade may be more than your GNP.
Mines are great defense. Almost as good as almost as good as just closing the stupid wormholes!
Try to conquer a race that breathes a different atmosphere than you. Great to transplant their colonists and turn huge domed colonies with 5 facilities into undomed colonies with 25 facilities.