For the record: You can refer to any guide for Twilight of the Arnor, as it's the same as EU.
What difficulty are you playing? The AI in GalCiv is one of the best there is, so don't just start out on 'normal' or above like you might with other games.
What galaxy settings are you using? What race? There are a lot of variables, but your first focus should be trying to understand the economy, as it's linked directly to your capability to keep peace and build a military. Try using someone besides Korx or Terrans, these two don't have the starting tech 'stellar cartography' which displays planets on the minimap. Having that tech greatly improves your chances of finding good planets.
Don't wait too long building ships. The AI looks at the 'military' graph, and if you're a no-show, it will start bullying you for money, then just plain out attacking. Even empty cargo hulls packed with the cheapest weapon can be an early deterrant - sometimes even a first offensive fleet.
With time, you'll see that the best way to deal with the AI is to overwhelm it quickly - there is a whole subculture here that focuses on 'zero year wins' - winning within the first 12 turns.
