When pressing shirts, it is easy to leave unsightly transfer creases and marks that will not come out. To prevent these creases/marks, place a Vapor foam pad under the shirt, cut it so that it is slightly smaller than the transfer, deckle the edge of the transfer paper by tearing each side of the paper (instead of a straight edge, you will now have a rough edge), and then press with just enough pressure to slightly compress the vapor pad.
-David Gross, Condé