If I were you, I'd install it dry. There are too many thin strips in that decal and the wet method could cause problems if the glass is wet.
Use the hinge method by putting a strip of masking tape on the top edge. Tape it to the window by the masking tape on the top, making sure the decal is positioned where you want it. Lift the decal up from the bottom, start peeling the backing paper off of the top but don't take it all the way off. Fold the backing paper down to the bottom edge , holding the decal off of the window with one hand. Start squeegeeing the decal down from the top with the other hand. As you get closer to where the backing is folded, pull it down some more and squeegee more. Once you have the backing pulled down to a comfortable level you can pull it off the rest of the way and finish squeegieeing the decal.