This is somewhat a tw@ of a job to do, but well worth it.

What you really need is:
- A Scalpel or sharp blade
- An Old credit card
- A Tiny, and I mean TINY, pin
- Tape measure
- A hair dryer
- Patience

First off you need to measure the widest points of the grill, side to side and top to bottom. Then on the back of your vinyl (should be white) mark up these points and cut out the square these markings should create. It may be worth adding a few mm incase of any inaccuracies.

Clean the car where it's going obviously, then peel back and LIGHTLY apply, light enough that you can pull it off if it doesn't line up.

Once you're happy that it will reach the edges then slowly use your card to flatten the vinyl on one side to the other - this is so you can peel back to fix any major bubbles, don't worry about tiny bubbles at this point - they are easy to fix later.

Once fitted it's ok to use the scapel to cut off any excess vinyl, don't cut to hard though as although it wont cause rust (bumper is plastic ) you shouldn't cut into the paint. After neating up the edges you can start with the little bubbles.

This requires the hair dryer and the pin, put on a low heat and pierce the bubbles, then flatten with the card, you wont see the pin holes as long as the vinyl is heated and the needle is tiny.

I know it's not a great walk through but it may help.