When I attended school for design years ago and applied to other schools some of them actually put out a list of things that they wanted to see from applicants. You could check and see online - I am sure there are some references - however a lot of them wanted to see examples of many different times of media. These days there will be an emphasis on a lot more digital programs, however , it is always great to know how to use old fashioned tools - i.e. pencil and paper, pen and ink, guache, water colour, acrylic etc and even experimenting with photography. Try out different media - even take a subject and do it in all of the media you have access too and see how you work with each one. You'll find out the ones that you like the most and it may even change your focus. Try different perspectives as well. Also - if you can find a "life drawing" class somewhere near you - attend some classes, they are great at helping you build foundation for your drawings - and if you should end up in animation or illustration will give you incredible strengths in modeling.