Exercise/activity in general seems good for mine. Actually, something involving bending down seems best. EG a bit of gardening. Yes, it hurts at first, but overall it does improve my back. The worst thing for it seems to be my job: sitting at a computer all day.
One thing I do every morning, and I'm sure it helps greatly, is a yoga posture called cobra. This stretches the ligaments in your back and 'unbends' it. Lie down on your stomach, put your hands palm down on the floor, by your shoulders, and lift your torso off the floor, trying to keep your hips on the floor. IE bend your back, backwards, like a bow. To start with, it seems impossible (which just shows how inflexible your back's become) but it will come with time. Don't do too much bend to start with, just be gentle.