The obvious thing to do is be pleasant and make eye contact with the interviewers! I would also suggest researching the company and brush up on your railway geography as well - one of the questions could probably be along the lines of a customer approaching you and asking how to get to some obscure station somewhere!
Also think of some examples of when you've given excellent customer service and a time when you've dealt with a difficult customer, and if possible give your examples in the 'STAR' format:
S - Situation. What was it?
T - Task. How did you plan to resolve things?
A - Action. What steps did you take?
R - Result. What was the outcome?
Good luck!