Tell them what it is about your work makes you feel good and don’t be afraid when they challenge you.They want you to be able to articulate what you’re work is about and what it means to you
References :
I interview people at Art College who are looking for a place.

Preparing a portfolio is a good way to organize student artwork, select the best from it, and have a record of the work done in high school. It shows the student’s ability and versatility. Generally portfolios are made by students who intend to go on to a career in art and must have a portfolio for admission to an art school. Whether students plan to attend art school or not, each one should have a portfolio simply to see the progress made in a course and to keep work together and organized.

Portfolios Are Organized in Two Ways

Examples of original artwork may be submitted, or slides of artwork may be shown. Three-dimensional, fragile, or large work would always be shown by slides. A portfolio for actual artwork need be nothing more than 24" x 44" tagboard folded and taped on three sides. Two pieces of foam core may be used instead of tagboard. Professional artists’ portfolios may be purchased at art supply stores or through catalogues.

Although some art schools prefer to see actual artwork, usually slides are used to apply for admission or advanced placement. If sending the artwork, send matted work that is similar in size. One disadvantage of sending the artwork itself is that it can only be in one place at a time, and you may wish to be considered by a number of schools.

What Should Be in the Portfolio?

A good portfolio should contain from 12 to 20 works of art. If a student has taken a number of art courses, a variety of media should be represented. Copies of published work are unacceptable. An interpretation of a masterwork could be considered, but paintings and drawings copied from magazines or photographs taken by anyone but the artist are just not done. Originality and creativity cannot be stressed enough. Size of the work is not important, though variety in media is desired. Consider including something less than perfect if the student has stretched and shown imagination. The following are the three important skills to include in a portfolio:

Drawing: a portfolio should have good examples of drawing in a variety of media such as pastels, colored pencil, magic marker, ink, charcoal, and conte crayon. A sketchbook could be included. The best drawings are familiar objects, people, nature, and architecture.
Painting: acrylic, oils, pastels, watercolor paintings. Drawings made with colored media could take the place of painting in the portfolio.
Design: include a poster, publicity flyer, photographs, or layout to show ability to combine a variety of elements.
The student may wish to explore one medium in depth and might have a large number of works that evolved in a given field of concentration (such as studies of the human form). It is best to avoid having work that only reflects classroom assignments. A student who is submitting a portfolio should show evidence of original thinking and depth. Quality is far more important than quantity.

What’s hard is trying to get your portfolio together. It’s not especially expensive as opposed to other colleges but it’s not cheap either. Click here for an idea of what AI in San Francisco will cost you: http://www.artinstitutes.edu/sanfrancisco/admissions_tuition.asp

You’ll find that if you are willing to learn–they’ll be willing to take you.
References :
http://www.teachervision.fen.com/teaching-methods/art/5951.html