You should try to stay on the defencive and build up your turrets and get the most powerful turrets in your current age.
The best turrets are:
Stone Age - Egg Automatic
Castle Age - Fire Catupult
Pilgrim Age - Small Cannons Then Upgrade to Explosive Cannons
Mondern Age - Double Cannons, forget the missle launcher
Futuristic - Either get the Blue Ion Cannons, or just save up for 2 super soldiers.
Hint - Keep healing special:
First you play an easy mode and evolve to the third age, then you let the enemy destroy you. Before you are about to lose use your special which heals the men, but be careful not to use too soon. when you lose play in any mode you wish to play and when you make units, they will have that healing special from the third age, but don't use the same special if you evolve to the third age.
Easiest way to win:
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.
Money and Exp:
Upgrade until you get to the last upgrade (future) adn get enough money to get all the turret spots and get 4 of the red cannons then if you have the patience to wait 4-5 hours, you'll have enough money to buy anything and DESTROY the cpu.
When you begin let alot of the other team gountil they stop coming then click on the special power and press pause then wait until it stops shaking then press pause again (Notice: will not work for lv 3).
Press a person when it's loadin press puase and they won't move but it still will be loading and ur guys will pop up.
Start the game by waiting until all (At least 5 men on the enemy side are created.) Then use your special to get enough money for the egg launcher.
Don't create units unless needed and build up money by your turret it's a big advantage.
When you have wepons like the fire launcher just pause it when it fires.
The weapon will reload and fire faster.