To apply a vinyl car window sticker, start by cleaning the window thoroughly using a microfiber cloth and glass cleaner until the glass is completely free of dust, grime and small fibers. Remove the back of the decal, press the vinyl decal onto the glass, and secure it with painter's tape. Using the edge of a credit card, press the decal onto the glass to remove any air bubbles. Remove the painter's tape and the decal cover slowly.
When removing the decal cover, be sure to pull away the cover at a low angle to minimize the chance of the decal peeling away from the glass. If the decal starts to pull away from the glass, replace the decal cover, and use the credit card edge to affix the decal to the glass. Then, attempt to remove the decal cover again. Although this process should remove all of the vinyl sticker residue from the car window, you can clean away any stray residue with an adhesive remover such as Goo Gone.
Avoid applying any decal during extreme cold or extreme heat. If you find any air bubbles after you applied the decal, use a needle to make a small hole at the center of the bubble. Then, use the edge of a credit card to force the air to the center of the hole, and press the edges of the decal into the glass.