Clean the application area and apply the vinyl using a wet installation.  Make sure the area is clean and free of dust, debris, dirt, wax, etc.

Some will choose to clean the application area with rubbing alcohol which is okay.

"Rubbing alcohol will not damage car paint if it is diluted to between 10% and 15%. Since rubbing alcohol evaporates quickly, it doesn't damage car paint."

Wet installs require one drop of dish or hand soap in a cup of water.  Apply to the vinyl so that the first attempt doesn't make the vinyl permanently stick to the surface.  Then you can slide it around and push out the extra water once it is in place with your fingers.

Try doing the install in the shade so it doesn't heat up the vinyl rapidly.  Keep a hair dryer around if you want to apply light heat to dry it out once properly aligned.  Otherwise you can park it back in the sun and let it all dry.