The key to a good suit, as with any item of clothing, is the fit. If the jacket is too big you end up looking sloppy, and if it's too small it looks like you're desperately trying to hang on to a time in your life when a slow metabolism wasn't on your radar. Get your measurements and buy a suit that fits. It's better to go big if you're in between sizes -- a tailor can alter it for you. Don't feel limited to only wearing it on special occasions. Breaking out the full arsenal on a Friday night just because you want to is never a bad move.
How to Fit a Men's Suit