Good advice by Justin.
I would like to add that you should really know your own work and be quick on the draw when certain questions come.
What might be a good approach is to present your portfolio to fellow designers, friends, students. Kind of a roll playing situation. Preferably people that might not necessarily know your work. They will point out aspects that might have slipped your mind.
This is less about you presenting a perfect portfolio and more about finding the right answers to the questions you will face.
This will help you to be confident in what you are showing. In my experience, it is how you carry yourself in the interview that will win the race for you. Being humble but confident goes a long way.