Here is a link I got from this board ages ago, that has helped me:
http://stylemakeovers.com/colortest/color_module.htm
It is for “doing your colors.” Yes, it is color, and yes, the examples are all women, but this is what you will get out of it:
–The right color shirts that will bring out your eyes; believe me, women notice when a man’s eyes looks beautiful
–it will make shopping easier if you know what colors look good on you. You can zero in on the colors you want, less looking and fewer mistakes.
As said before, line is very important, and difficult to see, because color and pattern are so in-your-face. If you have something that just hangs well on you, look for other things cut the same way. Don’t be pulled in by a nice pattern–who cares if it looks nice on the hanger, make sure it will look nice on you!
Men have this problem less than women, but don’t pick something that makes one part of your body look good, but makes another part look worse. The classic examples are leggings and tapered pants if you are at all heavy–your legs may look good, but your top only looks bigger.
For your hips, for example, go for a pant with a line that hangs straight down, and no pleats at the waist. You want to look at the line for the entire body, not just ankles-to-waist, and the straight line look makes the body line look long and lean. If you want to look taller or longer-legged, make sure your pants go to about an inch from the floor.
To emphasize the shoulders (my guess for what a muscular guy wants), the best neckline is probably boat-neck–there are a lot of sweaters cut this way. V-necks slenderize instead, because they continue the vertical and draw the eye to the face. You want the eye to get to the shoulders and stop. Patterns only at the top of the shirt or sweater also help.
Once you know a few things that make you look good, shopping gets much easier! It is worth it–people pick up on your self-respect, and that is the most attractive thing about trying to look decent.