Fit is the most important component of a man's suit. If you had to choose between fit, fabric and style, fit wins hands down. You can buy the best fabric in the world, put together by the best tailors in Savile Row, but if the suit doesn't fit, it won't look good.
Once measurements are taken carefully by the tailor, the suit must be manufactured so that your shoulders touch the end of the shoulder length and your upper arms do not bulge outward so there is a straight line from the tip of your shoulder to the ground. The chest length should feel comfortable against your body and is comfortable with the jacket buttoned. The lapels should sit directly on your chest and not bend outwards. If the fit is correct, sitting with the jacket buttoned should not feel restrictive.
The length of the jacket should be long enough to cover your back-side.
Accuracy in the pocket placement is critical to it's balance and appearance....
The collar should fit snugly around your neck and the upper back portion of the jacket should not have any creases or stretching.
The sleeve should go until your wrist bone, not to the begining of your hand and should leave a 1/2 inch to an inch of exposed shirt cuff.
Pants can be worn with or without cuffs and should fall straight down and follow the natural contours of the body without too much slack. There should be enough room in the crotch not to reveal anything. Generally, suit pants will not have any pleats, but if you do like pleats, one is enough.
The pants should be cut so they sit on the waist, not the hips.