If you have already upgrade your LG lucid to Android 4.0 ICS OS, You can take a screenshot without any 3rd party apps, Because the Android 4.0 has a build-in screen capture feature!
To capture your phone’s screen image, press and hold both the Home key and Power button for three seconds, or until you hear the camera shutter click.
or try “Volume down key + Power button ”
or try “Press the Volume up button + Volume down button” at the same time.
If you like to share the screenshots, Home Home screen, Go Apps > My Files > SD card >Pictures > Screenshots
You also attach the screen shot to text message from clipboard. If you like to send the screenshot via message, Lanuch Message apps, Tap and hold the Message body, It will pop-up “clipboard”, select the screenshot you want to share.
Wish this helps!