You want your fridge cold enough to prevent bacteria from forming but not so cold it freezes things. We've pulled out many a bunch of herbs and vegetables, only to find hardened, brittle leaves that got too cold.
Most articles we read suggested between 35 and 40 degrees Fahrenheit for the refrigerator. Meat is recommended safe anywhere below 40 degrees. We've seen varying temperatures for freezers, anywhere from the 0 to 2 degrees range (most widely recommended) up to 6 degrees, although that seems too high if you have ice trays or ice cream in there.
As is the case with a lot of ovens, the thermometer on your fridge may not be giving you an accurate reading. If you really want to be sure of the temperature inside, consider buying a freezer-refrigerator thermometer as a backup. (Here's one for $9.97 on Amazon.)
And read this article on Treehugger, which outlines other ways to keep your refrigerator running efficiently — like keeping it fairly full (more objects retain more chill) and vacuuming the coils.
You may also be keeping things in the fridge that don't need to be there, like soy sauce. Opening and closing the door for essentials that could be kept in a cabinet wastes energy.