Measure areas on the mixed media piece where you will affix the Mylar. Add the area measurements together and round up to get slightly more Mylar than needed.
Using the permanent marker, draw the shapes needed for the project directly onto the Mylar side that will face the art piece. Some Mylar has a color-coated side that you may choose to face out. Check the shapes' sizes with measuring tape to make sure you've drawn them correctly.
Cut the Mylar shapes out with a sharp pair of scissors. Wipe down each Mylar shape and the area on the mixed media piece where you plan to glue it.
Turn on a portable fan or ceiling fan and open a window to increase ventilation in the work room. Spray a light coat of multi-purpose spray adhesive on the side of the Mylar shape with the permanent marker outline. Wait 30 seconds while the adhesive sets up and becomes tacky.
Press the center of the adhesive side of the Mylar shape onto the cleaned area of the mixed media project. Smooth the shape onto the surface by slowly sliding your fingers outward from the center while applying even pressure. Let the adhesive set completely according to the manufacturer's directions before adding any more Mylar in the same area.