On the sprint optimus s main page (not in this rooting section) there is a sticky about roam control. That app will allow you to force your phone to remain in roaming, and thus save that battery.
http://forums.androidcentral.com/sp...pp-roam-control-optimus-no-root-required.html
Becides that, battery like has so many factors so is rather subjective. But for me this is what I do.
-Keep the screen brightness as low as I can and still see it.
-Set wifi settings to "Never" sleep, and use it at every opportunity (always shut of when you do NOT have wifi as this will in turn drain battery if the phone is searching for a wifi connection that is not there).