To help get over your nervousness, you may check around and see if anyone in your area is offering sessions on getting jobs. Many of these are free and include practice interviewing, where one person is the “employer” and one the “interviewee” and then you switch roles. If you can't find anything like this, get with a friend and have them ask those difficult questions. Go into it like it was real... get dressed up, bring your portfolio, etc. – whatever it takes to make it seem as real to you as possible.

Go over interview question possibilities and what your answers would be, so that you have ideas in mind for these questions already and don't have to try to think on the spur of the moment. Also write out questions that you want to ask them. If you don't feel that you really look the part, get someone to help you put together an outfit for interviewing. The main idea is that the more you practice, the more you do it, the more confident you'll feel and present yourself.