Carefully choose the correct size flag for the apparel you want the flag applied to.
What is the proper way to wear a flag on one's shoulder sleeve?
Left Flag versus Right or "reversed field" Flag
General Flag Rules do not specifically address the positioning of an embroidered flag; a decision is left to the discretion of the organization prescribing the wear. Some elect to use the "left" flag on both sleeves. If you are planning to wear only one patch, it is recommended that you wear a "left" flag on your left sleeve.
Military guidelines: To wear our country's flag properly, the field of stars is worn closest to your heart. Further, when worn on the sleeve, the flag should appear to be advancing and not retreating. Thus, if your embroidered flag is to be worn on your LEFT sleeve, use a left flag (normal). For embroidered flags worn on your RIGHT sleeve, use a "right" or "reversed field" flag. Source: Army Website FAQs.
For Polos, Uniform Shirts and T-Shirts:
1.5" wide for left sleeve
1.5" wide for right or "reversed field" sleeve
For Job Shirts and Sweatshirts:
2.5" wide for left sleeve
2.5" wide for right or "reversed field" sleeve
For Jackets and Coats:
3.5" wide for left sleeve
3.5" wide for right or "reversed field" sleeve