You definitely should have background refresh turned off. This causes certain apps to constantly update themselves even if you are not using them (go to Settings>General>Background App Refresh). Turning this off might result in a slightly longer opening time, but it definitely saves you battery.
Another thing you could do is turning GPS completely off.
Besides that, just wi-fi off if you are not at home, so it doesn't look all the time for available networks and maybe the brightness down. This should do it.