Have you ever created a skin that took you HOURS to shade by hand and then look at someone else's shaded skin that only took them a few short minutes and wonder, How does he/she do it?
Well, today, I'll be showing you how.

Materials
In order for you to make your masterpiece, you'll need to download Gimp!
You can get it from http://www.gimp.org/downloads/. 

You'll also need a shading template. For 1.7+ skins, I'd recommend using http://www.planetminecraft.com/skin/shaded-template18with-hat/ by PortableRogue. If you want to create a skin for 1.6 and below, you should use Kefka's Shading Template #1, which can be downloaded from http://www.planetminecraft.com/skin/shading-template-instant-shading-tutorial/. 

Lastly, you will need a skin! You can download one from anywhere or whip one up yourself, but if you choose to use a skin from someone else, make sure not to post it to any site and call it your own.

Steps
Step 1: Open up Gimp.
Step 2: In Gimp, press "File", then "Open", then click "Desktop" in the Open Image window and search for the skin you want to shade. When you find it, double-click it.
Step 3: In the bottom left corner, there is a small rectangle which says "100%" in it. Click in the rectangle and delete 100%. After doing this, type in "800%" to enlarge the image. If the image is too small or too big, type in a percentage that makes your image bigger or smaller. For instance, let's say that my image is too small at 800%. I type in "900%", and it is still too small. Then, I type in "1200%" and it's just right.
Step 4: Look on your desktop for the shading template you downloaded. After searching for it, drag it into Gimp and put it over the image already inserted. It should fit correctly, though if it doesn't, drag the skin template around until it does.
Step 5: Go to "Windows". Then, click "Dockable Dialogs" and then press "Layers". The Layers window should pop up.
Step 6: Click the number "100.0" next to "Opacity" and delete it. Replace it with "50.0" and the template will blend in with the skin.
Step 7: In order to save, you must click "File">"Export As" and then the "Export Image" window will open. In Export Image, enter the name you want it to be called in the "Name:" bar. At the bottom of the window, press the blue "Export" button and it will save to your desktop.
Step 8: Congratulations! You've made your very own shaded skin. Now you can show off your shaded skin that you made!

Any questions? Don't be afraid to ask me. Also, don't forget to click that diamond! -Opti