other than metho or turps you can get a solvent called 'prepsol' mostly from panel shops but possibly avail at super cheap etc.. this is what 99% of panel beaters use to remove the dbl sided tape holding car badges on, so it is guaranteed to remove vinal stickers without causing damage to paint work.
get an old kredit card, license, etc and use this as an applicator to firmly press the decal onto the plastic, this will help elimitnate any air bubbles.
If you still get air bubbles, use a pin and pop them then firmly apply pressure but only do this if you cant squeeze them out to the closest edge..