I started by drawing out a Dalek on a blank sheet of paper. I free-handed it, but you could easily print out an image from online.
Next, I transferred my image to the bag. I did this by coloring the back of my drawing with pencil and then laying the drawing on the bag. Next I traced over my image. This transferred the pencil to the bag.
Finally, I traced the pencil drawing with my sharpies. I added the word "Exterminate" to the side.
That's it! Don't you love the way I didn't iron my bag before I started working on it? I'm so classy.