As you've probably heard, body language is an important component of person to person communication. What you might not have heard is that your most important audience when it comes to body language might just be yourself. Yes its true, if you walk like a happy person, you might actually end up being happier.
We've already discussed environmental causes of poor posture, and your mood plays a role as well. And although forcing yourself to fake a better posture has been shown to have a positive impact, why not seek a more permanent solution?
Poor posture is as much about strength and flexibility as anything else. One of the reasons we preach postural work in our Fitness For Life philosophy is because its a good compass to a balanced body. So start paying attention to where your posture deviates from the "power posture" shown above. If your shoulders tend to round forward and your back has a hunch, you might have weak muscles in your upper back working in conjunction with tight muscles in your torso. If you tend to bend over at your waist you might have tight hip flexors combined with a weak core. Sometimes bad posture results from uneven strength. If the muscles in one region of your body are stronger than their antagonists in a mirror region, that might lead to an imbalance as well.
So start paying closer attention to your posture, and consult with a fitness professional on how to improve it