Originally Posted by b1gg13
I exit mine from the menu and this keeps gmail from updating throughout the day. If you just hit the back button it stays running in the background but Exit Gmail from the menu seems to kill it completely.
This is the step many people forget or don't realize. Properly "Exiting" or "Closing" the app will essentially disable it. Easiest and best step unless you don't want to use your Data at all then kill your data connection as stated above.
If you opt to turn off the data connection, still make sure you close Gmail app; it will suck your battery trying to connect to the server.