Draw designs onto paper. Use white/paler side if there is one, but keep in mind that design will be flipped once cut out.
Using a Sharpie or other permanent marker, add detail.
Carefully cut designs out and gently use a glue stick on the back.
Press designs onto selected notebook cover before glue starts to dry. Once pressed on, reapply glue on the corners, if needed.
Use adhesive transparent protective cover film to carefully seal and protect covers. Start on left side, near the spiral (if there is one), and gradually move to the right, folding over the right edge, into the inside of the notebook. If adhesive is sticking out on the top and bottom, fold those ends into the inside of the notebook as well.