You've probably all seen BetaTheData's custom NPCs 2.0. It's seriously awesome! Check it out here. So now you know what I'm talking about. This tutorial will be about changing the steve skin. It's not to hard when you have a good photo editing software. First you want to download the resource pack in the description of the video. Un-zip it and place it inside your minecraft resource packs folder. Navigate through the folders untill you find this page:

What you can do now is replace skinTexture with your skin. I don't think you can use hat layers, but be my guest to test it out. If you want to get an animated player, it's a bit trickier. First, have the original skin on a different layer of your photo editor so you know where to place everything. Start by putting your skin where the steve skin is on the new layer seperate from the steve skin layer. Then, replace the steve legs and arms to the right with your own. Finally, remove the legs and arms of your original character, as it will mess up if you leave them. To finish, delete the steve skin layer and override the old picture while saving it. Pop back into your world, and you should have some clones of yourself! The final product should look like this. If you can't get it to work, PM me and If I have time, I can try to make one of your skin! I hope this helped! (And no, this doesn't work on 3 pixel skins)