Summarize:

Make sure your iron is clean. If your shirt is 100% cotton, set it to high heat. If your shirt is a blend, use low heat.  If the fabric is cotton or polyester and your shirt isn’t still damp from washing, put your iron on a steam setting or have a spray bottle of water ready to dampen the shirt. Don’t use steam if the fabric is silk. Test iron a small piece of fabric on the inside bottom hem before you fully iron your polo shirt. If the high temperature seems too much for the fabric, lower the iron’s temperature. Lay the shirt on the ironing board. Fold the collar down as you would like it to appear. Make sure the collar is damp, then iron it gently. Turn the shirt over and iron the other side of the collar. Spray the collar lightly with starch and iron the collar again. Then turn the collar inside-out, spray starch again, and iron again. This will prevent the collar from curling. Use the point of the iron for the point of the collars and any corners. Use your hands to smooth the shirt down. Also smooth the collar down from the inside. You don’t need to use starch on the body of the shirt. However, you can if you want it to appear stiff, like a button down dress shirt. Lightly spray starch all over both sides of the shirt. Starch can leave white marks on clothes, which is one of the reasons for ironing the shirt inside-out. The other reason is that some fabrics are sensitive to ironing, and this will guard the exterior of your shirt from getting shiny or singed from the iron. Iron the sleeves first, one at a time, by pressing the iron down and smoothing the fabric from the shoulder towards the cuff. Avoid ironing over the edge on the shoulders, or it will form a crease. Next, go over the placket and shoulders with your iron. Iron the chest of the shirt by moving from the center placket towards the shoulders.  Your motions should be continuous. Don’t leave the iron too long in one place. If there are any patches or silk-screened logos on the shirt, avoid ironing those areas. When you’re finished with the top front of the shirt, set the iron to rest on its bottom feet. Move the shirt up so that the front middle is laid out on your ironing board. Begin at the uppermost part of the shirt and move your way downwards with the iron. Repeat this process for the front bottom of the shirt, working downwards towards the hem. Turn the shirt over. It should be on its back and remain inside out. Smooth out the wrinkles, then repeat the process on the entire back of the shirt. Check for wrinkles. Store it on a hanger until it is time to wear it. If you don’t have the closet space, you can fold the shirt.
Set up your iron and ironing board. Iron the collar. Turn the shirt inside out and starch it. Iron the top of the shirt. Iron the middle and bottom of the shirt. Turn the shirt right-side out.