i see, well then they stick on with the supplied two sided tape already on them i assume.
best prep for that is to COMPLETELY strip the area of any wax or contaminents.
wash area with dawn soap
clay bar area using soapy water or detail spray as lubricant
re-wash area with dawn and dry
wipe some rubbing alcohol or any other type of alcohol based paint prep/cleaner
make sure it is 100% dry
peel a corner of the paper off the adhesive, enough to stick the top or bottom to the car
put the decal in place, once your 100% confident where its placed, firmly hold it against the car and continue to peel the paper off, try not to rip or tear it
hold it about a minute to make sure it sticks
wait a day before getting it wet or dirty
make sure you re-wax your paint so it is protected
alot more involved than simply wiping off the area and sticking them on, but this will assure you that they are on there and will STAY on there