Always dress for success.
Be prepared for the questions by reading through your thesis,try to create some possible questions.
One of the scariest part is the possibility of not knowing some answers but its ok it do happen sometimes just deal with it as a challenging part of the situation,you just need to allow yourself sometimes to process the questions.You are not obligue to know everything though and expected to get perfect because as we all know defense is just for a formality thing. Try to slow your talk ,take a deep breathe,