An added benefit for any theatrical design and production student is to create a portfolio of their work. This is an organized and creative representation of who you are and what you have accomplished artistically. While the traditional printed portfolio is still an industry standard, creating a digital portfolio to present on a website, laptop or tablet is becoming increasingly important in order to remain competitive in this digital age.
Show your process. Document your work as you go through building a project, completing a design or a special class assignment. Demonstrating not just the finished product, but also your process, will show your interviewers how you approach and interpret a creative assignment.
What to include (varies between disciplines): Personal artwork that shows your skills, interests and impulses. Work from theatrical productions (ideally, conceptual drawings, process photos and finished production images). Paperwork from the technical side of theatre is also important to incorporate (wardrobe plots, drafting, light plots, samples from a stage management production binder or rehearsal notes).
Each piece presented should be clearly labeled with the production or class, your role in its creation, your supervisor/mentor/professor (if there was one) and possibly the materials and skills utilized. As your portfolio grows, think about what each piece says about you as an artist and what you can bring to the school or production.