Step 3: Step 3: Applying the vinyl
Once you've cut all the pieces you need, start by removing the backing paper of the piece you want to work with, and lay it adhesive side up on a workbench or table. Then take the trim piece and carefully lay it down on top of the trim to get the initial alignment. The adhesive is pretty forgiving, and can be pulled off and reapplied rather easily if you mess up.
Once you've got the initial alignment done, you can start working it around the rest of the flat surfaces until you get to the corners. Anytime you need to wrap around a corner or irregularity, you'll need to break out the heat gun. The vinyl responds very well to heat, so be careful and don't get it to hot because it will melt if you do.
To wrap around contours, heat the vinyl a little until it is soft, then work it around with a plastic card, making sure to clear any air bubbles that you get and avoid any wrinkles. Once you have reached the edge of the trim, you can trim the vinyl down to size, leaving about a quarter inch to wrap around the back side.
It helps at this point to notch the corners of the vinyl where the trim has a sharp external corner, and put a few slits in it anywhere the trim has a round internal corner, as pictured.
Make sure to use the heat gun when you fold the vinyl over to the backside, and it should hold extremely well once it cools.