Document Setup
The first thing you will need to do is set up the document that you will make the skin in. I've made a template document that you can download. If you only want one layer on your skin, click the first button. The second button is the template for a skin with two layers. Because Minecraft skins are 3D, every portion of the skin has multiple sides. I've outlined all of the sides with black on the templates to make it easier to tell where they are.
The above map is for a single layered skin. If you need to know where a certain part of the skin will show up on the actual character, this map labels the parts and shows the edges of each piece.
The above map is for a two layered skin. If you need to know where a certain part of the skin will show up on the actual character, this map labels the parts and shows the edges of each piece.
After downloading the template, open Adobe Illustrator, click Open, then chose the template file. Once the document is open, open the View menu. In the snapping options, make sure that only snap to pixel is selected. After that you are ready to start designing your skin.
Designing
The first part of the process is getting an idea of what you want your skin to look like. If you are making a skin of something that already exists, I suggest pulling up one or two reference pictures on Google.
Once you have your references and have an idea of what you want it to look like, its time to start designing. If you are making a skin that will include the optional second layer, I would recommend hiding all of the second layer pieces by clicking the eye next to all of the layers with a two at the end. It is so much easier to design a single layer skin and then work on the second layer later. If the layers are locked and you can't edit anything, just click the lock icon next to the layer you want to edit. this will inlock the layer and allow you to make changes.
The easiest thing to do is to just start by changing all of the different sections to their base color or the color that appears most often in that section. The face and the bottom of the head are usually skin colored and the rest is the color of the hair. Repeat that for every piece of the skin so that everything has a base color.
The next thing to do after that is to shape the clothes and add essential details. Base coloring just gets the right colors on the skin so now you have to make it look more like the reference. the easiest thing to start with is shaping the clothes. This means adding necklines to shirts and edges to all sorts of clothing. You'll also need to add a hairline to the face as well as any accessories they might be wearing that weren't included in the original coloring.
At this point the skin should be fairly recognizable. The nest thing to do is to add more detail. If you want to add a second layer to the skin, go and turn the layers back on so you can see them on your screen again. designing the second layer is a bit different than the first layer because you don't give it a base color. The second skin is usually only used for things like masks, hair details, hats, shoes, pant and shirt cuffs, glasses, and maybe jackets. Basically anything that stands off a bit in the reference picture.
The next step is going to be putting the basic outline of things onto the second skin. For instance if you were adding a pair of glasses, you would outline the glasses on the second layer and then delete any other pixels on the head so that they won't show up on the finished skin. There should be a lot of blank space unless you are adding a lot to the second layer instead of just small details.
After you've got the basic second layer set up, start adding more advanced details. This includes hair details, shadows, significant armor engravings, or anything big enough to show up on a Minecraft skin. This really just take a lot of playing around. It might take a while to get the exact look you're going for or you might get it on the first try. It honestly just depends.
After you finish, the skin, you'll want to press Ctrl + Alt + Shift + S. This will take you to the export screen. At the top, make sure it says that it is exporting as a PNG-24. This is very important as the skin will not work if it is exported any other way. Make sure you export it somewhere you will be able to find it later when you upload it into Minecraft.
If you would like to know how to put the skins into Minecraft, click the button below.