Regardless of how comfortable the interview may feel, remember that it is a first impression and too much information can backfire. Conversation should only pertain to the job opening and your qualifications. Questions of religion, nationality, race, gender, marital status should not be topics of conversation. If you are unsure or unclear about a question, it is appropriate to ask the interviewer to repeat or rephrase the question. It is better to answer correctly and communicate clearly than risk answering incorrectly.
Flow Let the conversation flow.
Be confident, not cocky. Don't let the conversation hit a lull. If there is an awkward pause, be prepared to ask a question, even if you already know the answer. Be polite and show enthusiasm. Also remember to thank the interviewer and send a written thank you.