Here's what you'll need:
A soup can
Some fine sand
A very sharp knife with a small blade
You can get everything you need but the soup can at most craft stores. I went to Micheal's Art's and Crafts and got the feathers, sand and hobby knife for a few bucks.
For the knife I used an Xacto hobby knife. Calligraphers use all different sorts of knives as their pen knives but the main requirement is that it be fairly short and VERY sharp.
Feathers. Most hobby stores sell turkey feathers. I got mine in a four pack for 2 dollars. You want them to be long, and check that the tips aren't crushed. Sometimes they are dyed different colors, this is fine.
I found pouches of fine sand at the craft store as well, I think they are for miniatures.
Step 1: Preparing the Feather
Historically, writing quills had some or all of the barbs removed from the shaft. A fully barbed quill is really a Hollywood invention. For practical reasons most quills had all of the barbs removed and the skinny end of the shaft cut off. This left something about the size of a modern writing pen that sat well in the hand. Some people used quills that used the whole shaft of the feather but retained the barbs on the end. This was really a matter of preference. I like to make this style, as I like how they look.
First you want to use your knife to shave off all of the barbs you don't want. You'll want to remove at least enough so that you can comfortably hold the quill without the barbs getting in your way. If you are making a barbless quill then just cut them all off and chop of the excess shaft.
Next, use the back of your knife or your fingernail to scrape all of the extra scale off the end of the quill that will become the tip. You want this to be smooth and even.
Now cut off the very tip of the quill, just the solid round end. Then use a long thin pokey thing (like a straightened paper clip) to clean out all of the dried membrane material from inside the shaft.
Step 2: Tempering the Quill
Fill and empty soup can with fine sand, then heat it in the oven at 350 degrees for around 15 minutes. Then carefully remove the can (it's hot!) and thrust your quills into the hot sand as far as they'll go. Now wait till the sand cools off. Your quills should now be tempered.
Step 3: Cutting the Tip
The first cut I make is fairly straight cut from the top of the barrel at about a 45 degree angle, this determines the end. Next a make a long shallow cut on the bottom. The shallow cut should not reach the other side, you want it to run out straight to the end.
Next you make the third cut, about halfway down the second cut in the bottom. This third cut will roughly shape the tip. After that you make the channel split. The channel will help hold the ink and guide it to the tip. It should be straight and about the same same length as the second cut. Try to get it as close to the center of the tip as possible.
Finally you finish the tip by carefully trimming the tines on either side of the split so that they smoothly curve to the tip, then trim of the tiniest bit of the tip to square it off neatly.
Step 4: Writing With Ye Olde Quill Pen!
I hope this has made sense, please feel free to comment with questions.