Switching to 3G helps with battery life if you aren't using data heavily, this is the biggest improvement when I need my battery to last.
Turn the screen brightness down, or on Auto brightness.
Buy a spare battery, I carry one all the time. Between the two I can go 20 hrs. or so with moderate usage between charging. eBay is great for it, an OEM Samsung battery runs $12-$15 shipped or less. Don't buy chinese chit.
They don't call this phone the CHARGE for nothing.. it uses some power but the data speeds in 4G are insane and the screen is beautiful!
Good luck, enjoy!