The most important thing a guy should look for is fit and proportion. When clothes fit properly you will look great. Also, it important to avoid things that don't help add to a more streamlined look. Pleats and horizontal stripes are bad. Also, larger prints and plaids don't help. Make sure things are well scaled. It's important to find a slim and short a pant as possible because just shortening a longer pair of paints does not usually work because the proportion of the knee and leg opening won't work. Also, don't wear shirts untucked (unless its a Peter Manning shirt!) if it falls any more than a couple of inches below your waist.