Use a solution of about one tablespoon soap to one spray bottle full of water. Spray it on the area where you are going to apply the vinyl. MAKE SURE THE ENGINE IS COLD (i.e. don't drive the car before you plan to put on your overlays).
Then carefully position the overlays. The soapy water will allow you to slide them if they don't line up perfectly at first. Once you are happy with the placement, use a hair dryer to dry up the soapy water and use a squeegee (sp?) or even the flat side of a credit card to gently push out the air bubbles.
If you take your time and are patient, it will turn out perfect. Don't get frustrated if something doesn't line up right away.. just use some of the soapy water to let you slide it into position.
Hope that helps. Post pics after you get them installed