"Yip, yip, yip, yip." That's what you'll be saying all night if you're going to be one of the martians on Sesame Street.
What you need to do: Get styrofoam for the eyeballs and pipe cleaners for the antennae. You will also need lots of material to drape over yourself. You'll need to make sure the mouth area is a black mesh material, so you'll be able to see from the inside of the costume. More instructions here.