Ice packs/Stretches. At the start of back pain, you should utilize heating pads or ice packs (whichever feels better to you), anti-inflammatories (like advil/motrin/ibuprofen), and stretching (touch your toes). As you start to feel better, doing crunches and core exercises will help take the pressure off your back and prevent a recurrence. If you have any numbness or tingling in your legs, see your doctor immediately!
Keep active. My recommendations: stretch by laying on your back and pulling one leg to your chest, hold for 5 sec., repeat with the other leg, do it 12x on each side. Strengthen by laying on your stomach with arms stretched out in front of you, lift right arm/left leg and hold for 5 sec. Repeat the other side, do it 12x on each side. Ice the 1st 48 hrs, heat thereafter, never more than 20 min. Per hour.
Stay active. It is important to keep active. Don't sit for long periods of time, walk as much as you can, and don't lie in bed for long hours. Do some gentle back stretches, and apply heat to the area. You will probably benefit from medications also. Start with nsaids, like Naproxen sodium, or ibuprofen. If the pain gets worse, or you have pain going down into your leg, be sure to see your doctor.