Do: Look up and out. Greet the world. Exude relaxed confidence. Be your height. Smile.
Avoid: Looking down. Hiding your face in your phone. Projecting vulnerability. Slouching or hunched shoulders. Looking distant.
Self defense starts with not being an attractive target. You may not be feeling great everyday, but when out and about, don't show it. Channel your inner Master Thespian (search SNL archives for Jon Lovitz). As a side effect, smiling actually induces changes in the brain that will make you feel happier!