It is very likely that you will be interviewed by another person, along with the first interviewer, and that you will be asked very similar questions to those in the initial interview. Repeat everything from the first interview that got you to the second.
Remember to share your eye contact with all interviewers, not just the one you feel comfortable with. Also, answer the questions fully again, the other person has not heard your answer.
You will probably be asked more questions regarding your personal skills and specific interests at the second interview, be prepared for more challenging questions and try to back up your responses by examples and facts. It is essential to remain composed, do not flutter and take your time it is important that you can effectively communicate your opinions.
The second interview is your opportunity to ask questions, which you were probably hesitant to ask at the first interview, for example issues regarding salary, bonuses and training schemes.
Although you have been selected for the second interview, and it is probably between two or three people, be careful to remain practical and do not be over presumptuous assuming that you are the successful candidate, there is a fine line between confidence and arrogance. Competition for most jobs nowadays is high and it is crucial to display good manners in a confident but unassuming manner.
Bear in mind that the second interview is your opportunity to showcase your intense interest for the job and this is demonstrated by everything you say during the interview, your sole objective is to convince the employer that you are the right candidate for the job.
And remember to take your CV again!