Clean the area thoroughly with rubbing alcohol or soap and water. Do not use Windex or similar products because it will leave a residue behind that will prevent the sticker from adhering well.
Remove the decal from the backing paper. Measure and place the sticker in the desired location.
Once the sticker is firmly in place on the desired surface, carefully rub the decal in place with a felt squeegee or a credit card wrapped in a sock. Start at the middle and then work your way out to the edges.
Slowly peel the thin front transfer tape from the decal leaving just the cut out vinyl decal behind.