How exactly do you skim fat off of liquid that you want to use to make sauce or gravy with?

If I'm in a hurry I lay a paper towel on top of the gravy and quickly remove it. If you want to remove more fat, lay on another piece. Quick and it works every time.

Thank you - all good suggestions! If I can I do stick it in the fridge to harden, but yesterday I needed to make the sauce right away. It was, shall we say, a learning experience :)

To expand on the post to Smaug where I discussed the fat skimming cup, my favorite way is to strain out the bulky ingredients and let it sit for one or two days. The fat hardens and literally peels off the stock. I make mine in a 6.5 slow cooker, so I wouldn't use the cup unless I just needed a small amount immediately.

A deep, fine mesh conical sieve is perhaps the best tool. I like to line it with cheese cloth, place it over a deep stock pot and pour the liquid through the sieve. A small amount of fat will still get through in fine particles no matter how much you skim while it's cooking. If you don't need to use it right away you can refrigerate overnight

A spoon or ladle is what usually comes most readily to hand- it's kind of crude, though, you end up either leaving quite a bit of fat or scooping up some of your liquid. Some people also use an ice cube, usually wrapped in a paper towel, which will pick up fat pretty readily in small quantities. There are cups with a low spout designed for pouring off the fat, but I've never used one. The most effective, if you have time, is to chill the liquid until the fat solidifies on top, where it is easily removed.

I use a spoon or a ladle. Sometimes I dump this stuff into a glass jar, let any of the sauce settle to the bottom, then pour off the fat into my fat can (eventually destined for the garbage). Then I can recoup the small amount of the sauce remaining.