The sport coat and jeans look is a pretty popular look for men, but not everyone can pull it off well. You'll see men wearing sport coats that are too big with button up shirts or jeans that are too long, or sport coats too light in color to properly complement the ensemble. It's important to learn how to pull off the look in a way that is both casual and stylishly sophisticated at the same time.
Select a casual fabric. Traditional sport coats have too much sheen and look too formal to wear with jeans. Choose softer-looking fabrics such as twill, corduroy or a linen blend.
Tailor the suit so that it has a modern fit on you. The fit should be comfortable, but tailored to your body. The shoulder seams should end exactly where your shoulders end. The sleeves of the coat should be exactly at your wrist. If you are wearing a button up shirt, your sport coat should reveal 1/4 to 1/2 inch of cuff. The jacket should be shorter at the waist than the typical suit jacket. Place your hands at your sides. The fit is right if when you cuff your hands, the bottom of the coat sits inside your hands.
Choose well-fitted dark jeans. Dark jeans have a clean, neat look to them and can match with pretty much any sport coat color. If you really want to go with a lighter jean, choose a medium wash and wear a dark colored jacket such as black, brown or navy blue. Wear a thick belt with an attractive buckle, but not too much detail.
Pair the jacket with a skinny tie. A regular tie looks too formal. Wear the more modern skinny tie, which is about 1/2 inch thinner than the typical tie. Otherwise, you can wear the jacket without a tie and the collar unbuttoned.
Tuck in button up shirts. Tucked in shirts look much neater and go well with the look. If you chose to forgo the button up shirt and tie for a t-shirt, you can leave it untucked. The shirt should not be longer than the sport coat.