Here is the way I do it. Just happens to be what works for me.
The picture has most of what I use. These items can be found around the house. The only thing is the sanding jig which I made myself. Funny thing is that I made about 8 prototypes till I settled for the very first one. It is nothing more than 2 each pieces of wood, any size will do, and two pieces of thin aluminum sheeting. A hinge holds the wooden pieces together at the bottom. The key to the sanding block is to make the pieces of aluminum meet together with a little force. This holds the feather with the proper amount of pressure. Notice there is a gap at the bottom of the wood blocks. This seems to force the aluminum sheeting into position.
Remove the feathers from the wing. I save both primary and secondary. I have found a sturdy pair of scissors works best. Then I wash the feathers in the bathtub. This is mostly to remove the dirt and blood. Any mild dish washing liquid will do. After I give them a thorough rinse, I shake them dry and then let stand for a day. Then sort the feathers by left and right wing.
Snip the quill at the base to remove the unnecessary portion. Now tear the leading edge (short side) of the quills off. Save these for your fly tying friends. They make great tails, legs and antenna. Now place the feather in the sanding jig and then mount the jig in a bench vise. I take a sharp knife and trim the quill base lengthwise. Then I use a file and with gentle, soft, angular strokes work the quill down to a flat and consistent thickness. This will all take a little practice and most likely you will destroy a few feathers. When you reach a point where it starts to look like a full-length fletching switch to sand paper and a sanding block (that’s the long piece of plywood under the sandpaper).
You can store them whole or cut them however you desire.
The last pic is staged just for the forum. I would normally trim the feather prior to putting it in the jig. It makes the feather easier to work with.
The feathers in the picture are from a recent hunting trip I took to Scotland for Pink Foot geese.
I hope this helps. Jack