Rub the sticker to be sure the transfer tape is properly adhered to the sticker.
Clean and dry the desired area. Stickers will stick best to clean smooth surfaces.
Remove the paper backing slowly making sure the sticker stays adhered to the transparent transfer tape.
Carefully position the sticker to the desired area. Once the sticker sticks it will be nearly impossible to reposition without destroying the sticker. Rub the sticker from one side to the other, eliminating any air bubbles.
Use a hard edged object like a credit card to make sure the entire sticker is fully adhered to the surface.
Slowly remove the transfer tape. Making sure no part of the sticker remains on the transfer tape.
Check for air bubbles. In most cases air bubbles can be worked to the edge of the sticker, but if not, a pin hole will allow the air out and become virtually invisible, once the bubble is gone.
In most cases, the applied decal can be removed by picking at the edge of it, and then peeled off the applied surface. In some cases. like with particularly old decals for example, a flat razor blade may be needed for careful removal.
Clean and dry the area under and around where the decal was. Glass cleaner, degreaser, or a sticker-removing fluid can make this quite easy.
*Note: Vinyl decals are intended for one-time application. Instances of successful re-application are lucky and quite rare.