I installed Rally Armor's basic mud flaps a few weeks ago. The instructions they provide a pretty good, but they provide then in black and white. Print them off in color as it will be easier to figure things out. For the instructions, they installed the flaps on a red car and all the hardware is black, so its easier to see where things go. A red car printed in black and white looks black, so its hard to make out some of the diagrams. I suggest starting with the rears as they are more difficult. I also found it easier to just remove the rear wheels when installing the flaps in the back.
Step 2 of the rears has you remove a bolt. It looks like a screw, but there is a nut on the other side. The nut is held in place by a couple plastic tabs, which are fine as long as you apply light even force to the bolt. I tried to use a hand drill to get the bolt out and broke the plastic tabs. DO NOT DO THIS. If you do, you'll have to find a way to wedge a wrench, pliers, etc. to keep the nut from moving around and there is not much room to work with back there. I had to find places for a screwdriver, flashlight, a set of pliers, and two hands; this was not easy. Also, this area is right next to the exhaust, so let your car cool down first.
Step 6 of the fronts has you making an additional mounting point by threading a screw into the liner. I found it easier to drill a small hole first, then thread the screw into the provided insert.
Other than those two points, my install went pretty well. It took me forever to install the first rear flap because it took me a while to realize I had broken those plastic tabs.
Good Luck,
Kevin