-show competancy at different things, not just all the same of one thing. for instance, if you include models of characters, try to add non-characters as well perhaps, or a range of different looking characters/styles
-try not to show 100 angles of the same model/s
-try and show some distinction, that you have your own style

most of that is probably obvious though, and i don't know how important it all is for a uni course