1. Besure to clean the area really well.  It is a good idea to clean with a cleaner with alcohol base.
2. Hold decal in the areas you wish to make sure it will fit with no obstructions.
3. After you have decided where it will go, you can peel off the backing and stick in place.
4. Rub the sticker really well to make it adhear to the surface. 
5. Start peeling off the transfer tape from one corner to the other very slowly. If the sticker starts to come up, just rub it down and peel slowly.
6. After the decal is in place, do not wash it until it sets up, about 3 hours will be fine. 

                  If this is a large decal, you may want to use two people to make sure you get it lined up strait.
                  You can also use masking tape to align the decal.