Volume bar blocking parts of the screen shot For Android 4.0+, an easy way to take a screenshot is to hold down the power button + volume down at the same time.

However, using this method, I often get the volume bar showing and blocking parts of my screenshot. Is there a trick to making this work without screenshotting the volume bar? I've tried many different techniques.
If you are familiar with the android development tools, you can connect it to a PC and use 
adb shell screencap -p /your/path/screenshot.png 
to take a screenshot and store it on the device. If needed, it can be transmitted to your PC using
adb pull /source/path/on/device/screenshot.png /target/path/on/PC/screenshot.png.

But if you want to keep it simple, the best way is to first press the volume-down butten and immediately afterwards also press power. Keep both pressed until the screenshot is taken. It requires a few tries, but if you manage to find the right timing, your screenshots will be perfect from that time on ;-)