Step one of applying a sticker is to always make sure you're working with a nice clean surface. You'll want to make sure that you remove any debris or dust and also allow the surface to properly dry.
Almost all of our stickers have Transfer Tape which is that clear layer on top of the sticker. This is used to easily line up and apply the sticker. If you have a Slap Sticker, there won't be any transfer tape, but this step will be the same.
Peel away the Backing Paper from the sticker, leaving only the sticker itself (and transfer tape).
Line up where you are wanting to apply the sticker to, ensuring you have it leveled how you want it (not on an angle).
Push down on the centre of the sticker. It is best to use a squegee or card to apply pressure evenly, starting from the centre and pushing outwards. Doing this from the centre will help remove all the air for a smoother finish. Once the sticker is firmly applied, give it a nice once over with the squeegee while the transfer tape is still there (if it has transfer tape).
Now that the sticker is on there, you might be thinking it looks weird with the rectangular clear layer over the top. Grab a corner of the clear transfer tape, and peel it off the surface of the sticker.
When doing this, it is best to peel it back as close to the surface as possible, as if you were almost folding it back on itself. If you pull the tape perpindicular to the sticker, there is more chance for it to create air bubbles by pulling the vinyl off the surface.