You have to strengthen your muscles to have better posture. The old trick of walking around with a book on your head can actually help. When you are sitting on a bench, couch, chair etc… don’t lean up against the backing. Sit, not slouched, with your back straight. It’ll help build those muscles. Simple yoga can help as well.

To know if you have good posture photo yourself standing and sitting as you would normally (no posing). Better yet video tape yourself. Many many people think their posture is good before they see a video.

In regards to the low back pain, i’d have it checked out by a doctor. Sometimes there are physical causes that need surgery. If there isn’t one then you can explore alternatives like chiropractics, acupuncture, massage, yoga, etc…

My mother learned, in her days when she danced in the movies, to imagine a string from her head to the heavens. It pulled her up. There are also shoulder shrugging exercises. (Push shoulders back gently while standing and try to get shoulder wing bones closer to each other. Keep abs tight and knees soft.)

Also watch your head and neck. Ask someone to check to see whether your neck is sticking forward like a turtle. That is bad.

A good PT can teach you exercises and ergonometric tricks. Lumbar support, etc.

Also, this posture chair is good as well. It looks like it puts pressure on your knees, but it doesn’t. It actually evenly distributes all of your body weight properly. When you sit in it, your back effortlessly assumes good posture.

http://www.amazon.com/Ergonomic-Kneeling-Posture-Office-WL-SB-101-GG/dp/B000TMFSQK

@squirbel: For me, that chair is a killer. It may help some problems, but I am better with both back and lumbar support (a pillow or rolled-up towel.)

If you are really interested in correcting your posture long-term, I suggest taking some yoga classes. They will help you to both understand what good posture is and to strengthen those essential back muscles.