SMILE!

You're never fully dressed until you wear a smile.
You can choose to wear a scowl or a smile. The smile uses less energy and fewer muscles, and is heartily recommended. The smile is contagious. The smile will get you smiles back.
The scowl is off-putting. The scowl will get you . . . well, you'll notice people cross the street when they see you coming.
Of all the things you put on, no matter how spiffy or polished or buffed or pressed they may be, none is more important, none will make a more lasting impression, than a smile.
A simple turning up of the corners of the mouth can do wonders for how you feel, and how others feel about you.