Do not stay in one place for too long even when you are behind the cover.

Your enemies will eventually destroy wooden boxes and sandbags, leaving you vulnerable to attack.

Complete levels to earn gold stars, which you can then use to unlock new missions.

Adjust the crosshairs on an enemy's head, if you are using sniper rifle, before popping out from behind cover.

Good thing is to wait for an enemy's health bar to appear before shooting.

To jump onto a gun turret you have to press the icon located at the bottom of the screen.

Whenever your character's on the move, press the right and left sides of the screen to avoid objects.

Don't forget to claim daily rewards, as this is a great way to score supplies without spending your hard earned currency.

Earn free gold by completing different requests, like following Glu on Google+, watching trailers on Hulu or signing up for a variety of services.

Look for the "Get Free" button on the in-app purchase screen.