Formal menswear, such as a tuxedo, usually includes a vest as an accessory. When dressing for a formal occasion, it's essential that all your outfit's elements -- from the slacks to the shirt to the jacket to the vest -- are worn correctly. Part of this involves ensuring the dress vest's belt or strap has been properly adjusted. An improperly adjusted vest can make you look sloppy, or larger than you are.

Put on your pants and dress shirt. Ensure the pants are already correctly adjusted. To adjust the vest belt correctly so it looks as good as possible, it's important the clothes the vest will be worn with also fit properly.

Lay the vest down on the flat surface so the vest is flat, without wrinkles, and the back of the vest with the belt is facing up.

Disconnect both sides of the vest's belt. The left side has a strip of fabric and the buckle, while the right side is only a strip of fabric. The buckle is made with two pieces: a square or rectangular piece of metal and another piece of metal in the center of the first piece of metal.

Pick up the left side of the belt with the buckle with your left hand. Pick up the right side of the belt with your right hand.

Pull the belt's right side under the buckle's right side. Pull the belt's right side over the middle of the buckle, the metal bar separate from the buckle's square or rectangle metal piece. Pull the belt's right side under the buckle's right side until there is about 1/2 inch to 3/4 inch of the belt's right side pulled beyond the buckle.

Put on the vest. Look in the mirror. Ensure the vest is buttoned up and the vest's front is overlapping the pants' waist.

Grab the buckle's right side that has been inserted into the buckle. Pull the buckle's right side through the metal buckle until the vest fits snugly across your stomach, the buttoned front does not gape and you look slim.