It's all in the Prep!!!
every job is 70% preperation,
so first of all make sure your surface where your going to put the stickers is dry and dust/dirt free.
peel one side back a little bit to help you position the sticker to the surface, make any adjustments before pelling the rest of the backing paper off.
Once in place hold the sticker taught and use a credit card type tool to push the air out vertically up and down in stroke susing a slight angle.