In a multiplayer game, expect a rush. In fact, it's very easy to start a rush in Dominion.
      It's hard to counter a rush, but you can do so build as if you were going to rush yourself.
      Your immediate priority is defending yourself. Worry about cool technology after you've
      got a wall of troops.

      The computer AI has a tendency to strike back after an attack. Always leave a few guys
      behind when you go looking for action. Similarly, when you rebuff the computer's attack,
      mount an immediate counter-offensive.

More tips...

                    -Be aware of your unit effectiveness against various targets. There is nothing
                    worse than charging into the enemy only to realize his unit is invulnerable to
                    small-arms fire.
                    -Watch for engineers sneaking about. In general, your base should be ringed by
                    cheap infantry on all sides--not just the side facing the enemy.
                    -The AI is fuzzy about sending units to help out even when its buddies are being
                    slain nearby. Whenever you hear combat, make sure valuable assets are
                    actually helping out.