In my experience in meeting with reps and listening during portfolio critiques, it is in my experience that many art schools prefer a break down like this:
10-12 pieces will effectively demonstrate your portfolio
They like to see examples of:
- Usage of typography
- Illustration
- Ad design and Page layouts
- Still life pieces (done not in a Graphic Design program, but a fine arts one) (Also, having pieces done involving the human body do not hurt at all!)
- Photography
- All of the above done in a variety of mediums (gouache, watercolor, pastel, marker, colored pencil, graphite, illustrator, photoshop, etc.)
Obviously this list will be tailored to what sort of school you’re attending. If it’s an animation and video program, you might have to provide examples of illustrations, but in some semblence of sequence (as in doing an illustration, but breaking it down into 9 steps, and in each step showing the process of how to make coffee with a coffee maker or something thereof).
If you’re truly afraid that your portfolio is lacking, call the school! Look the number up on their website and get ahold of a rep. They will more than happily set you up with someone who can review your pieces with you and let you know if you’re lacking anything. That way you can complete what you’re lacking, come back, and get accepted! Easy peasy right?