Making a portfolio

I am thinking about submitting some original cartoon artwork to a local animation company. Any advice on how to build a nice looking portfolio, I have very small amount of knowledge on the subject, and I don't want to walk into his place looking like a fool! Biggest question I have is first what size pictures should I include in portfolio (thinking 9x12) and also should I color my cartoons. I was going to include two pics of each of my cartoons, one being pencil original and the other was going to use colored pencil any advice would be AWESOME!!!