Using it smart.
Turn down brightness.
Turn off 4G if not needed for long periods when the phone is idle.
Turn off wi-fi unless connection is stable.
Turn off background data and gps.
If you need an app to keep the phone almost dead at idle, you can try to Juice Defender or the such, but people tend to have mixed results with battery apps.
My best recommendation other than just installing Basix, or Exodus (and eventually the custom kerenel, which will help quite a bit with the battery) and doing the things I said above, is to go and grab one of the cheapo extended batteries from ebay or batterybay (or mugen if you want to drop 100 bucks) deep charge the hell out of it, and enjoy.