If you’re using Android 4.0 or above, Follow the below steps.
Just press and hold the Down Volume and Power buttons at the same time . You’ll notice an animation on the screen , indicating that the screenshot was saved. Android will save the screenshot to your Gallery. Launch the Gallery app and tap Screenshots to view and share your screenshots.
If you are using Android 2.3 or above, then follow this trick
Press and hold the home key for 1sec and immediately, press the power button after a vibrate release both button,then your current page will be snapped
*You can find your screenshot in sdcard/ScreenCapture
You have to press the home button for almost 1sec (before task manager comes up)then press the power button almost simultaneously and after a vibrate release the butons immediately.