Do everything you can to prepare for the interview. If you can, research the company and write done some questions to ask about it (anything but pay, time off or benefits!)

Spend some time rehearsing how you will answer questions. Think about specific accomplishments you have had in your career to date. You want to use specific examples of your performance in your answers to questions.

Close the interview. Regardless of how you feel, ask for the job. That is best. If you are not comfortable with that...close with "I really want this job and would be great for it because...."

Be sure and send a thank you -- even to a placement agency!