Taking screen shots on android phone:

 Android phones offer a great feature by which we can take the screen shot without using any 3rd party application. However the screen shot android tricks vary from one android version to another version.

Press the Home button + power button (This trick work on most android phones.)
For Galaxy Nexus: Power button + volume down button.
For Galaxy Note 2 and S3: Swipe your palm on the screen to take screen shot.