I've had back problems for a large part of my life, due to an old rugby accident. First and foremost, the best thing you can do is stretch every day. Stretch at least once, in the morning but preferably two or three times. Stretch as if you are stretching your legs out, because this stretches your upper body to and it loosens your hips which in turn loosens your spinal column.
If your back is really sore one day, lie on your back with a heat pack underneath, and then go for a long walk as it will loosen you up. I would avoid chiropractors, are really good massage is the best thing.
To strengthen, do proper situps, back arched exercises. Hope that helps.