First you have to decide where you want to put the mat. If there are any nuts, screws, wires, harnesses, you will want to avoid covering those areas because you might need to access them later. Also think about whether or not you can cover the area up in one single piece. If not, you can cut the mat into pieces.

Clean up the area. I would use soap and water to get the dirt off...then some kinda solution that will remove sticky residue, oil, or grease. Then press on the mat. You might want to remove a bit of the contact paper instead of removing the whole sheet because itll be hard to move around a big sheet of sticky mat. I usually peel the edge off, then apply it onto the metal, then pull the backing off of it as I am pressing the mat on the metal.

After the area is covered, make sure there are no bubbles. You want everything to be in contact with the metal. You can use a rubber roller or anything else you can think of to press the mat onto the metal really well.

Some people like to heat up the matting before applying it because it is more flexible. Have fun.