Click the images to enlarge.
You will need a google account for this (sign up for one here).
Step 1: Sign up for a account at minecraft.net if you don't have one (free or premium does not matter).
Step 2: go to http://mineshafter.appspot.com/ click login and log in with your google account.
Step 3: Hover over your google username or email then click settings.
Step 4: When in there connect your minecraft account in the Connect Username bit so it looks like the screenshot blow.
Step 5: Go to http://www.minecraftskins.com/ choose a skin and click the button.
Step 6: Then go to http://imgur.com/ click login and log in with any account you want but i did it with my google account then upload the photo
Step 7: Copy the Email & IM url and paste it to the skin url box on http://mineshafter.appspot.com/ and click set.
Step 8: Go to the download page what is on the Mineshafter site and download the "Windows Proxy Launcher" and "Mineshafter Client Proxy". For non-windows don't download the "Windows Proxy Launcher".
Step 9: Put them in a folder then open the Proxy.
Step 10: A Minecraft Launcher will open and Log In with your Minecraft.net account then Enjoy.
If you want to come to my server press here to find out how. Link