I did mine a couple of weeks ago and I think they came out nice. I learned some important tips along the way.
1. Use french curves: go out to the local art store and pick up a set of 3 differently sized transparent french curves. The reason you want to cut the fender edges with curves is because the door edge trim you apply when your done doesn't like sharp corners. The smoother the curve the better. I measured horizontal and vertical points, found the perfect curve angle so the apex hit the straight line. I would then mark the two points on the french curve itself so when I carried it over to the opposite fender I would flip it over and line up the same dots. This ensured that the curves were identical on both sides.
2. Cutting: after I taped and marked off the curves I wanted, it was time to cut. the outer fender is plastic riveted to the inner wheel well liner. I found it was best to separate the two. It's a PIA but without the wheel liner getting in the way, you'll have a better time cutting. If you leave the wheel liner in, the blade of the jigsaw sometimes hits it and causes it skip and give you problems with the cut. In terms of the jigsaw itself, use a variable speed one. Too fast and you'll melt and clump the plastic. Too slow and you'll be cutting forever. The trick is finding the right speed. Use a high tooth count blade, preferably for plastic but a metal cutting blade also works.
3. Wheel Liners: with the wheel liner out, you'll cut along the lines and think your doing an amazing job, then you mount it and your left with huge gaping holes in the back
I thought for sure that I had done something wrong, but then I realized that the factory liner bends out at that point and no matter how you cut it, your going to be left with the hole. I then realized that its plastic and could be reshaped. I hit with a heat gun and used a hammer to push it back and hold the position by leaning against the tire until it cooled.
I did that for a while and eventually I got it to curve back in and cover most of the gap
I did the same thing for the back. Most guys just remove the back wheel liner but I reused mine, by curving it back it looks good, you can hardly notice it and it protects the Jeep.
Overall its fairly easy to do, just take your time and you should be fine. When your done just file down the edges smooth and get some edge trim from your auto parts store. It looks like this