Once a computer opponent has located your empire, you've
got to be on your toes. The AI is especially good at
striking hard and fast where you're vulnerable, so you've
got to have a sizeable fleet ready to intercept any attacking
foes before they can do too much damage.
Don't spend your time chasing a fleet; try to predict where
they'll head and meet them there.
The best defense is a good offense; use scouts to locate enemy
planets and hit them before they can hit you.
Let the computer micromanage research and construction; it's
usually pretty good about building this fast, and it frees you
from the hassle.
You definitely need a good mix of ships to win a battle, from
escorts and destroyers to the heavy capital ships. Balance is