This guide is to help you make some pixel art from pixels you may have. First off, I suggest downloading Gimp and monkeys minecraft color palette.
So, first load your image in Gimp and select monkeys palette. Then push + until you can see the individual pixels. Then find the color in minecraft. There are 32 colors in minecraft, with or without shadowing. Then you just copy each pixel into a mc block.
It's easy as that! Happy spriting,
-Spartan