Not sure about the video part of it, but here's my tip on the graphic design part of it. I read somewhere that about 10 pieces is good for a portfolio. Sprinkle your very best and most impressive among them so that they're not all up front or at the end. If you don't have that many samples, create them. For instance, pick a product (real or imaginary) and create a design that sells it. And like Hoof said, don't put in anything you're not proud of. It's better to have fewer pieces with a lot of impact than to have a lot of pieces that are only so-so.