I have done this a few times. Here are the steps I follow….
Air and surface temperature must be above 55 degrees Fahrenheit for the application of the vinyl.
1. Measure and mark the area you wish to apply your vinyl using a water-soluble pencil. Precision marking will help assure a level application. At this time, take your decal (paper and all) and tape it to your predetermined area. Stand back and make sure it is straight and looks good where you have it.
Adjust as necessary.
2. Spray the surface under the decal with water (put 2 drops of dish soap in 1/2 qt of water) or application fluid (I recommend the application fluid_
http://www.ags.com.au/store/group.asp?GroupID=450&CategoryID=72 ) While the decal is attached to the surface by your tape, carefully peel off the backing paper. The decal should stay stuck to the application tape at this time. With the application tape still intact, squeegee the decal to the surface by applying pressure with smooth even strokes. Start at the middle of the decal and work your way out to the left and then the right. Note: Before you squeegee make sure there are no wrinkles in the decal or application tape.
3. It is a good Idea to wait just a couple of minutes before you remove the application tape. This allows the application fluid to dry some and will prevent the decal from trying to come up. Once it is adhered to the surface, squeegee the entire decal a second time. Then carefully peel the tape off the entire decal.
4. It is common for there to be some small bubbles throughout the decal. These bubbles will leave by themselves within a few weeks. If you have any major bubbles you can eliminate them by carefully heating the area with a hair dryer or heat gun, and then puncturing them with a needle and applying pressure with your thumb. Note: You can do more damage than good by chasing the smaller bubbles. They will leave by themselves as the vinyl breathes and the application fluid evaporates.
And as other have said... patience is a must!