A. Take It from the Top
A good suit should hug your shoulders, not slouch off them. Most guys think they're a size larger than they are— 42 regular instead of a 40. When buying a suit, go ahead and try sizing down. When you pull on the jacket, there should be a firmness to it. You should snap to attention and stand taller.
B. Lose the Flab
Think about the width of the sleeves. Sometimes having a tailor slim down the sleeves of excess fabric is all that's needed.
C. Show Some Cuff
Your suit sleeves should end just above the hinges of your wrists, so a quarter to half inch of shirt cuff shows.
D. Taper, Taper, Taper
Your jacket should contour to your body. Have a tailor nip it at the sides. This will accentuate your shoulders—whether you've got strong ones or not.
E. Break It Down
We like flat-front pants, with very little break at the ankle. This produces a long, clean look. Your pants should just clip the tops of your shoes, not bunch up over them.