Smartphones operate on a sort of spectrum. On one end you could put battery life, on the other end all those options like wifi/3g/sync (among other things). If you want great battery life you can't have those on all the time. If you want those on all the time, you won't get great battery life. It is best to find the compromise that works best for you and what you want most out of your phone.
Here are a couple of things that you could consider - adjust the screen brightness, do not use live wallpapers, switch off networks when not in use (WIFI, Bluetooth, GPS), adjust update intervals for widgets (do you really need twitter/facebook notifications every half hour?). You could also consider downloading a battery monitoring app such as JuiceDefender.