You will need:
Yarn in different colors.
A Cross Stitch pattern
A crochet hook. (I used size H)
You can get cross stitch patterns of anything, and you can even make your own.
I took a picture of the robot from here, and put it into Gimp. I used the mosaic filter to make it into a pattern.
Step 1: Following the Pattern
You start the pattern on the bottom right hand corner. First row you go right to left, second row left to right, 3rd row right to left, etc. You should leave your tail on your piece until you are finished, that way you always know that that is the bottom right hand corner.
Note: I printed my pattern too small. When you print it make it big, so that you don't go crosseyed counting squares.
Step 2: Crochet Away
To change colors: (Look at the pictures)
Put you hook through the stitch. Instead of pulling the current color through, put the current color on top of your stitches, and grab a new color. Put the tail of the new color with the old color. Pull the new color through your stitch, and continue finishing the stitch.
In the video I show you how to change colors.