Modern lifestyles aren't particularly conducive to having good posture. We sit at work, slump on our sofa, collapse into our cars, and generally don't spend a moment thinking about our spines. Nevertheless, we should, because having good posture is more important than you think.
Posture isn't just about looking trim or elegant. Bad posture can affect your circulation and cause spinal deterioration over time, while good posture relaxes your back, prevents chronic fatigue, and protects your spinal disks. It can even keep you be pain free at work.
If it's so harmful, why do so many of us suffer from poor posture? It's not actually a sign of laziness, rather it's a combination of weight, genetics, stress, unsupportive shoes, and myriad other factors.
That doesn't mean that bad posture is inevitable. If you're sitting, try keeping your shoulders back and your head directly forwards, not titled up or down. (Having the right chair and computer helps with this!) Sit with your knees slightly below your hips and your feet flat on the floor, without crossing your legs or tucking them under. While it may take some time to get used to a better posture, your back and neck will eventually thank you.