How to rule the galaxy through might alone.

 
The Conqueror focuses on taking other players planets.

Once captured,
you use the money from these new planets to upgrade even further. You end up with lots of ill gotten colonists and planets this way. They make money for you and you will quickly build an empire similar to what a Builder might be able to create.

Be sure to stock every new planet acquired with plenty of Fighters and Torpedoes to be sure that the former owner won't come and try to take the planet back.

The conqueror strategy (when effective) produces a large number of colonists in a very short period of time. However, you become hated quickly, and its very difficult to defend your new planets.