The Perfect Fit

You could have the most expensive suit on the market, but if it doesn't fit properly, you're going to look like a farmer. A suit should be neither too tight not too loose, it should gently hug the body, but not restrict you in any way.

A suit jacket should pull smoothly across your back when buttoned. the lapels are meant to lay flat across the chest. Some padding in the shoulders, can help fill out your frame. Needless to say, there is no one style that works best for all men. Take your time. Do your research. And whatever you do, trust the mirror. No matter how much your wife or girlfriend (if you're still shopping with your mother at this point, finding the right suit is the least of your problems) tell you how amazing you look, if you aren't feeling it, try something else.

The English Fit 
The British have a rich tradition of impeccable tailoring. While Savile Row has changed significantly over the years, there's no place like it. English suits tend to fit close to the body, accentuating a defined waist, strong chest, and naturally sloping shoulders. These features are exaggerated by the British taste for double vents that flare at the button of the coat. High armholes, rim sleeves, and tapered pants only add to the lean look. English suits tend to hug the body without feeling, or looking, tight.

The Italian Fit 
Europeans developed a very different suit with a high, padded shoulder and longer jacket. The Italian suit drapes more than the British and is accented by narrower pants, which are often wore much higher on the ankle.

The All-American Fit 
Classic American style emerged in the 1950s with the Ivy League look. It reached it epitome in the sack suit, a three-button model that is more forgiving than the tailored looks from across the Atlantic. This Brooks Brothers look has lower armholes, three uttons, and a natural, sloping shoulder and is generally more relaxed and informal.

source: Details Men's Style Manual by: Daniel Peres