Using an Iron: When using an iron, use the cotton setting.Press on a hard surface using a bit of pressure (not a folding table or ironing board.) Press and hold, pick up iron and move just a bit. Be sure to move it just enough so that the preceding steam holes are covered. If you see parts that are still opaque, repress. It is not hot enough. There is such a thing as too hot as glue will start to dissolve into fabric.
Do not place iron or heat press directly onto a design. If the foil cover sticks to the shirt, you can pick it off with tweezers. The heating element got too hot.
You can color different parts and portions of your garment with the foils by cutting and dividing the colors. Crumple, wrinkle and wad up the foil before pressing for a distressed design. (Does not work as well with designer foils.) You can then leave it as is or proceed with the next tip. After distressing one color and pressing (and removing the foil), immediately press another foil over the distressed design giving a layered look. If you add one color on top of another without distressing, it may pick up some pieces, not pick up others and it may wash off. Therefore, placing a foil on top of another must be intentional because it may be picked up by everything it touches. Removing or erasing the color is not an option so carefully plan before pressing. Distress the bottom layer of foil in other ways giving different looks, maybe use a stick or draw hashmarks into the foil first before pressing it onto the garment with the adhesive. If you want to hold the foil in place on your garment, use the leftover design carrier sheet. Be careful to only use it on the color up side, not the silvery foil. It will remove the coloring. Just cut it up with your scissors.