It seems that I am constantly reminding my two boys to sit up at the dinner table - posture counts and people are watching how you carry yourself. Sit up straight, move with purpose, and look everyone in the eye when you talk to them. NOTE: sorry, went into a little parenting rant there. Please forgive me...
I also find myself constantly reminding my athletes that posture counts when you are lifting, doing body weight techniques, and even stretching. Putting your body into the correct, well aligned, and "stacked" position allows you to be stronger, safer, and create good body awareness. Unfortunately most people sit way too much in their car, behind the computer, or in front of the TV. We're talking about the majority of the day in a position that puts tremendous stress on the spine and puts connective tissue into a position that cause compensations that lead to pain, tightness, and even injury.
So what can you do to combat this? First and foremost is to move and move well! Learn to pay attention to how you move and how your body reacts to load and positioning. Second, and almost as important, is to work on your mobility on a daily basis. I don't mean that you have to spend hours on it because a few minutes will do wonders.
Want a simple way to loosen up your neck, shoulder and chest? Check out this video by Max Shank to see a simple and effective technique to make you sit taller and feel better in a matter of moments.