How do I compile a successful portfolio?

At this early stage in a design based or creative education, people are not looking for specialisation - they are looking for the opposite. A successful portfolio will have variety, no two projects should be the same, or of the same medium. At least one project of modelling, sculpting, digital work, painting and drawing should be the minimum. However well you may paint with oils or sculpt with clay, if that is your entire portfolio then those you are presenting it to will not know whether or not you can interchange between media, and at this point that is all they want to see. You should also include work that you don't like - this gives you a chance to show that you can acknowledge when something has been unsuccessful and how you have learned from it. Each project should have a clear narrative and should be carefully put together. You should know the design process and the story of each project extremely well so that you can present the portfolio like a work of art in itself.