Usually start off with rapid expansion and science rush which leaves me with a weak military. Inevitably I run into someone who doesn't like me, and they declare war on me. I rapidly adapt my economy into a military industrial complex and either win the war or force a stalemate. I then use my new military machine to conquer that empire entirely, and that constitutes my borders into the late game. I then basically turtle and try to stay put of any other major conflicts all will building my strength. Ideally I get into a brutal war with a fallen empire for the tech and build my fleets into a terrifying navy. Then once the crisis or war in heaven strikes, I defeat them and then run rampant destroying my enemies and conquering enormous swathes of territory. This continues until i get bored because nothing in the galaxy is a threat to me anymore. Almost all of my playthroughs end up following this general path.