what makes up a stong body of work?

Take your time and think about what you want to present in your portfolio. Try to remain consistent with the work you provide so they get a feel for the direction you are going. Presentation of your work is important and shows you care about what the viewers will be seeing. Take good pictures of your work with no distractions such as a painting hanging crooked, or things in the background that take away from your work. Originality is something they will look for as well as talent, your ability to create work from ideas you have come up with. I also agree with David that getting serious opinions of your work from those other than yourself or your friends, will help to guide you forward. If you know any other artists that you respect and appreciate (artists that are trying to make a living at it), allow them to view your work as well.

I would suggest you ask one or more of your teachers to critique your works. You might also ask at some local galleries if they would mind giving you a hand. The worst they could say is no. At best you just might make a friend who would give you some insight. Remember tomorrow's artist is their future as well.