There are many things you need to manage throughout the battle to win against the enemy. If you're slightly negligent then the enemy will overpower you, so be watchful and use the best tactics. You will need to make decisions about building of troops, upgrading your base and which advanced weapon to use in a situation.
It is highly recommended that you patiently go through the instructions in the game and play in the Easy mode to begin with. Then you can take up the challenge to defeat the enemy in the more difficult modes of play. Good Luck...