Before I start anything, I'd like to clearly state that most of what I learned about working with fake fur, I learned from matrices.net. Things that I learned from there that I post here will be linked back to that site, though not necessarily to where it was said, so you'll just have to trust me that it's in there. So let's start.
~ When working with fur, fake or not, do not cut it with scissors. Ever. This will cut the actual fur and you'll end up with fur shorter or even missing in some places. Use a razor knife and cut from the back. * Meaning turn the fur over so that the fuzzy side is facing the cutting surface, and cut using the razor knife on the underside. Do this with even extremely short furs, I know from experience (Ammy mask) that that makes a difference.
• On the back of the fur, before cutting it, draw arrows indicating which direction the fur lays in. * Check and double-check this before cutting, I've messed this up a couple of times. About ninety percent of the time, you can get away without doing this, but that last ten percent of the time will come all at once when you're almost done and running low on fur. Again, just trust me. It's better to mark it than not.
• When working with white fur, use a light-colored marker for any markings on the back. This depends on how thick the fur is, but it's generally a good rule. I ended up using a lime green Sharpie after the red one bled through on my Ammy mask.
• Light colored fur will take Sharpie ink. Meaning if you have a light-colored fur, and you want to make it a dark-colored fur using a permanent marker, you can. However, it takes a fair amount of marker to get total coverage. If you want to dye a large area, you'd be better off buying the color fur you want right off the bat, unless you can't find it.
* The asterisk indicates stuff I learned from matrices.net.