1. Clean the surface, preferably a window. Isopropyl alcohol works great, cleans and dries quickly. 

2. Peel the backing off the decal, leaving the decal attached to the transfer paper. The backing is the stiffer material with the grid pattern. The transfer paper is like masking tape. So, you're only removing the paper with the grid at this point. 

3. Carefully Align and Apply the decal, press evenly to prevent bubbles. 

4. Use a squeegee or a credit card to rub out any bubbles. Try to start in the center and press out. This will also firmly apply the decal. 

5. Last step, remove the transfer paper. Go slowly and press against the back side to ensure all pieces remain on the glass and aren't pulled up. Corners and sharp edges tend to want to curl up, so pay close attention.