It is common practise for an informal chat to take place before the formal interview starts. Do not make the classic error of assuming this is not part of the interview - it is. It is part of a professional interviewer's assessment. However it is also an opportunity for both parties to overcome any initial awkwardness. Some very informal questions are likely to be asked - i.e. how was your journey? Did you find us OK? etc etc. Do not become over familiar or over friendly and do not go into a long story about how terrible the traffic was. Answer with short friendly reply's - i.e. "the traffic was quite bad but I allowed for that in preparing my journey". Always initially address your interviewer using their salutation i.e. Mr/Mrs/Ms. They may well address you by your first name - do not take this as an insult, it is general practise. If the position you are applying for is of a senior nature then it is not unreasonable to address the interviewer by their first name also if they address you in this manner. It can be a good idea during some interviews to ask the question "how would you like me to address you during the interview" if you are unsure how to address your interviewer.