If you notice that your stickers are starting to peel off of the surface, here are a few helpful tricks.
First, make sure to dry off the surface before applying the sticker- this removes any residual moisture and oils that may be working against you.
Second, make sure you apply it at an angle (i.e., peel off both corners).
Third, use a credit card or squeegee to smooth out any air bubbles that may occur in the adhesive layer.
Finally, allow 24 hours for the adhesive to completely seal onto the surface before touching it.
So this is how to make a sticker stick again.