It really depends on how you are using your phone as to what you can do to preserve battery life. The following link gives a few pointers from Apple on how to get the most out of your battery life. http://www.apple.com/batteries/iphone.html
Voice roaming on and cellular data on.... these are the defaults, so they're ok. Biggest battery eater... display brightness. Go to settings/brightness, leave auto-brightness on and slide down the slider to as low as you find comfortable. This slider reflects the minimum brightness to whatever maximum you set (mine is at about 25%). Note that if I'm outside, I do turn up the brightness if necessary, but under most conditions 25% is more than adequate.
The other culprit is the GPS and I would suggest that unless you're plugged in, use sparingly cause this will also eat up the battery.
And finally... Make sure you have a solid WIFI connection. If you're WIFI is spotty and drops in and out, the constant connect/disconnect will also eat up the battery. If you do have a spotty connection on WIFI, then go to WIFI settings and disconnect and forget the connection. Of course you could simply just remember to turn off WIFI if you're not using it ...even with a spotty connection, but for me having to remember to do this is a pain.
You may want to go into settings > location settings > and turn off anything that you don't use with locations (Facebook, etc). It has also been advised to go to location settings and turn off most of the "system services" because sometimes these can affect battery life dramatically.