Quoted from High_End_Pins:These are typically installed here on empty cabinets so the first step to doing it well would be pull the playfield out.You can set up a workbench right next to the game if needed and that way you can just pull the wired playfield and put it to the side of the game.
Other than that make sure that you lightly scuff only the area that will be decaled so you can get any dust nibs out of the surface in order to make sure the decals go on smooth.
Test fit them prior to removing the backing.
Apply them.
Now run felt down the entire length of the playfield wood edge and rails on both sides.
Gently place the playfield back in the game and you are all set.
Can I ask you what kind of felt you used and where did you purchase it from? Is it a certain thickness?
Dan