This trick works only on few phones not all Android Phones.
Phone: Xolo Q800
OS: Android JellyBean 1.4.2
All you have to do is press the
Power Button + Volume Down Button – Same time
Screen shot will be store in the Memory card automatically. You can see the screen shots in Gallery.
Exact path would be SDCard/Pictures/Screenshots
Some screen shots that I have taken from my Phone:
Screen shot 1:
Screen shot 2: