Buy a turret, preferably "second" turret like the egg launcher and fire catapult, 
although you should always go with the explosive cannon. Allow enemies to close in
to your base, and build either a single infantry guy, or a infantry/archer team. 
They will kill the maximum for their gold by being within range of the turret, and
will die long before getting in range of your enemy's turret. You may not have 100%
life by the end because of enemy archers, but it is the easiest way to win.
Also: The Ion cannon turret = win button.