a couple tips are
1. get a heat gun, the stuff molds around anything with a little heat. the heat also makes the material much stickier.
2. get a break away blade type razor knife. the long blade that you can snap off a little piece at a time. and get a bunch of blades. the stuff will gum up the razor blade pretty quickly and then you can just snap the blade and have a clean cutting surface. Also dont buy a cheap plastic one- buy a nice metal one with rubber on the handle.
3. get a formica roller, about 10-12 bucks at home depot, its a 3" hard rubber roller on a metal frame that you can really lay into to press the fatmat down with. the fat mat comes with a small wooden roller but that thing is junk and you WILL BREAK IT.
4. buy a box or two of latex or nitrile gloves, the stuff sticks very well to your hands and the oil/dirt in your skin makes the stuff less sticky.
5. template complex shapes and if you cant get a piece to form into somewhere just slice it and patch in a piece over it.
6. clean the car out, vacuum all loose debris up and just before doing a section I would wipe with denatured alcohol- let it dry then stick to the clean surface.
7 when applying start at one side of the piece of fatmat and work slowly- pushing all the air out. when you get an air bubble stuck in a section just poke it with the razor knife, let the air out, apply heat and mash the material down with the roller.
8. if you have any friends with patience and skill offer to buy the beer, this job takes a LONG time and 4 hands are better than 2