Check the care instructions for the item you are planning to adhere the patch to. Make sure they are clean/recently washed.
Set your iron to "Cotton" at 400 degrees for about 5 minutes.
Iron the area you are planning to place the patch.
Place your patch into position with the design facing up and place a cloth over it.
When the cloth is covering the patch, press the iron down firmly for 20 seconds while moving in a slow circular motion.
Turn the item inside out and iron the back of the patch for 20-30 seconds.
Let it cool for about a minute and then test to see if it can be lifted. If it can, repeat the previous step.
If you want a more permanent solution, sewing is always the best option. Do not use with bleach. Do not use on fabrics that you can't iron, such as nylon, vinyl or leather, as they have a low melting point.