Buy plain clothes in plain colors that you feel comfortable in.

and make sure they fit.

Get some shoes that are in style. Nothing sticks out more (to me anyway) than dirty running shoes in a non-workout setting. If you get anything white get some Magic Eraser, shit is amazing for keeping them that way.

1. look what normal people wear
2. pick up similar clothes with your choice of colors and size
3. ????
4. fuck hot women

H&M is a pretty popular chain store found in many malls. You may look like a total bandwagon motherfucker, or asian premed student, but the prices are cheap and solid colored shirts never go out of style...
A nice pair of Vans are always also good. Chukka-lows tend to look pretty great. Although a skater will be able to look right through your scuff-less shoes, no one else will.
Good luck, Joe...

Oh, and shop with a girl who knows fashion.
Maybe search Tumblr for a fashion blog by someone who lives in your area and tell them your blight. Maybe ask for advice, resources, or for them to meet up with you and take you shopping. After all, how threatening could meeting up in a Mall cafeteria be?