In our resources section you will find a range of articles discussing posture and ergonomics. Here follows an excerpt from such an article:

What is proper posturing? Well, one cannot lay down hard and fast rules for proper or correct posturing as all our bodies are made differently from one another. The nearest possible definition that makes sense is "that position of the body which is least demanding on the body structure, its joints, bones and muscles". That is, in the right posture, the weight or the stress of doing an action will be equally distributed or absorbed without causing any excessive strain on any single part or joint of the body. A person working with the proper posture will be able to work for long hours without feeling tired or fatigued, while somebody following a wrong posture has a more likelihood of getting bogged down quickly, and in a worse case injuring oneself in the process. Recent studies have revealed that most of the back problems that occur in young/middle aged people are due to bad posturing only, and not due to any injuries due to accidents or any diseases.

So, in the very basic level, the solution is pretty clear. Follow a healthy posture habit in order to keep one's spine or back healthy. That is, while sitting, take care to keep one's spine always straight. Also, make it a point to stand up and walk few steps daily, for a break, or consider taking a short jog in the evening. Such activities are effective in relieving lower back pain.