You can find guidance on the proper wear of the Army Class A uniform in Army Regulation 670-1, Wear and Appearance of Army Uniforms and Insignia; and Army Pamphlet 670-1, Guide to the Wear and Appearance of Army Uniforms and Insignia. The regulation provides instruction on when it's appropriate to wear the uniform. The pamphlet provides detail on how to wear the uniform and includes guidance on the placement of ribbons and badges.
Differences in Dress
The Army includes the Class A uniform in the service category consisting of the Class A, the Class B and the Dress uniform. The Class A is comparable to a suit. For men, the uniform includes a short or long-sleeved shirt, long tie, slacks and blazer/coat. For women, it includes a short or long-sleeved shirt, neck tab, slacks or skirt and blazer/coat. The Class B includes all of those elements except that the coat; neck tabs and ties are optional when soldiers wear the short-sleeved shirt. The Dress uniform is the same as the Class A except men wear a bow tie and women wear a skirt.
Updated Policies
In 2008, the Army switched from the longstanding green service uniform to blue. This includes the Class A. Officers and enlisted personnel had until July 2014 to buy the blue service uniform. Due to the uniform's higher cost, enlisted personnel received an increased clothing allowance to offset the added expense.