I always use a squeegee to apply stickers and decals; air bubbles and uneven adhesion be gone! You don't need it really if you're careful; I just use it because I have one lying around. The trick is to check twice on the location and orientation of the decal before applying and when applying start adhering from one side to another as opposed to just plopping it down to prevent any folds, wrinkles or airbubbles.