For 13 I play aggressively, taking the small ones around me at the start and using the majority of my forces (make sure to send enough) to take their medium and large bubbles when they are weak (when the enemy is spread out). Try to hold back the strong attackers and stall them while you go straight for their important bubbles, don't bother with the large neutral cells until they are weak.
Later on, try to connect your territory and start pushing forward using two or three large armies and finally surround them and take over.
 "Bullseye (Interstellar Marines)"){kind=icon}
 "Nano War"){kind=icon}
 "Hit The Jackpot 2"){kind=icon}