2v2 coop games have no particular strategy. The only way to win is to raise your income faster than the enemy.
In any other gamemode i would ussaly let the first 3 waves pass and increase my income. In all v all u should time yourself untill you need to start building towers. A solid defence for the fist few rounds would be a EMP with either 3 upgraded gun turrents or 1 lv3 cannon tower or 1 telsa tower with one lv2 cannon tower.
It is important that u should have a tower that deals splash damage. This is because 1 telsa tower lv1 wont be able to keep up with a cluster of fast novas. this can cause a storm of weak monsters to break past your defence.
One of the main things that can help you is tower preferances. They are auto set on strongest. Each tower has a good preference that can be used effectivly. Its up to you to determine what you want them to be.
If you are pinned down and you rapidly must defend yourself, stop defending and start saving. If your life drops below 10 it pretty much means that your screwed. If your able to save enough send out a powerful creep. The enemy will see the treat and will be forced to defend. This will open a chance for you to attack.
