Stage one is pretty simple to master, just make Clubman, Slingshot Man, Slingshot Man, repeat.
When you have enough money for the Dino Rider just use Dino Rider, Slingshot Man, and repeat.

Stage Two. Its pretty much the same strategy just use Swordman, Archer, Archer. When you can afford some Knights use Knight, archer, repeat.

Stage Three. Use Dueler, Gunman, Gunman. When you have around 2000 money buy a Canon, Gunman,Gunman. Don't forget about the special attack! That should bring you some more money. Just do the same thing until stage four. TIP: DON'T USE MORE THAN 3 GUNMAN IN A ROW, they will be cut down by Duelers and cannon and that many of them are just a waste.

Stage Four. Use Melee Infantry, Infantry, Infantry, and repeat. I don't suggest using the Tank.

Stage Five! There are TWO ways to beat this sucessfully way ONE and way TWO.

ONE - Use Godhand, Gunman, Gunman. And when you can afford some vehicles, use Vehicle, Gunman, and repeat until you win.

TWO - (Way two is my personal favorite). Use Godhand, Gunman, Gunman. When you have around 50,000 buy the next two turret placements. Then buy the turret which cost 40,000. Use the same Godhand, Gunman, Gunman, until you can buy another one. When you have bought a second one you shouldn't have to buy anymore units, your turrets should handle it for you. Wait till you have 100,000 and buy the turret which cost 100,000. Now your unstoppable. Save until around 200,000 money and use Special Attack then buy Godhand, Supersoldier, Gunman, Gunman. And win the game.