A great deal of importance is placed on formal military attire, worn by servicemen and women at both military and civilian functions. This formal attire is considered the equivalent of a civilian tuxedo, and each branch of the service has strict requirements when it comes to dressing. Each type of uniform has a manual, detailing the correct dress code, which includes how to pin the different types of medals to the uniform.
Arrange the medals in order of category and rank, as detailed in the Uniforms Manual. The highest ranking medal should be on the top left, as you look at it from the front, or the top right from the wearer's perspective.
Slide the medals onto the mounting bar in order. The Uniforms Manual will detail how many medals per bar, but you should space them evenly to ensure each bar appears full.
Position the top bar according to its position in the Uniforms Manual, usually above the left breast pocket, and push the pins all the way through the fabric and lining of the jacket. Fit the spring-loaded pin locks on the inside of the jacket to hold the bar securely in place.
Pin the next row of medals underneath the top row. The Uniforms Manual will give exact instructions on positioning multiple rows of medals, but the rows should be situated so the medals overlap any ribbons below them, and only the medals themselves are visible on lower rows.
Use the breast pocket seams as a measure to get the mounting bars straight. The Air Force uses ribbon insignia instead of medals, though the process for aligning them, ranking them, and pinning them to the uniform is the same.