Use masking tape on the corners to position the decal.
Apply masking tape through the center of the graphic.
Remove the masking tape from the corners of one end.
Lift that half of the graphic up and remove the backing paper.
Cut the liner with scissors, and discard it.
Holding the decal away from the wall, use the squeegee to press the vinyl to the wall, working from the masking tape toward the edge. Remove all other masking tape. Repeat on the other side.