What Oleg said, and in the settings use an small quadrant, with 4 AI races ( so you don't have to scroll in the diplomacy window
) dificulty Hard, AI bonus in medium.
Don't use neutrals, they are trouble to the AI and a bonus to you.
Chose the AI races manually, so you make sure you don't get any "friendly" AI, like the Cue Cappa or the Toltayan.
The AI always fight better on small quadrants.