Perfect your posture. How you carry yourself communicates a lot to other people, so make sure you're telling them that you're confident and in-charge. Keep your shoulders back, your spine straight, and your chin high. Walk with purpose instead of dragging your feet, and sit up straight. When you look like a confident person on the outside, you'll be approached as one by the world around you.
You won't only fool everyone else -- you'll fool yourself too. Recent research shows that the positioning of your body cues your mind to feel a certain way -- so positioning yourself confidently will make you genuinely feel in charge. And to top it off, having confident body language has been linked to lower levels of stress, too.[1]