I think the best thing you can do in an interview is to create rapport/connection with the interviewer. It's great if they start off with "small talk", as it makes you more relaxed and also gives you a chance to find a common interest etc. Apart from that, body language... mirror what the interviewer is doing, sit the same way, same expressions on your face. That has remarkable power, makes them feel you are really interested in what they are saying..
Handshake, not to hard and not too soft. It city chic a clothing shop? Maybe personal presentation will be important.
Do some preparation before you go. Read through your resume (sounds silly, but it helps) and remind yourself of all the great things you've done in the past, and all the personal qualities that you have that the employer needs. Even if it's not work related eg. I've been a mother, could be translated to mean, I can handle many things at once and can prioritise my tasks efficiently.. something like that lol. Milk your experiences for all they are worth!!