According to a column I just read, there are three main areas to prevent and possibly correct low back pain: posture, weight and exercise. The article, Eliminate low back pain, is well written by a Physical Therapist (not a demon Chiropractor) and contains valuable information.
I have found it helpful to do the stretching exercises my physical therapist recommends. Do some core strengthening exercises, such as the ones highlighted at The Mayo Clinic. By keeping your core strong, your back won't put itself in a position to cause that sciatica pain you are having.