Answer:
This is a competency based interview question where they are looking for evidence of you having used the competency of the ability to set priorities. To answer the question you should use the CAR format.
C = context - What was the situation
A= Action - What did you do
R = Result - what happened as a result of the action that you took
You should check out the competencies that are required before the interview using the job advert and the person specification. So if the advert says they need someone with the ability to work as part of a team you will be asked to provide evidence of how you have done this. Prepare your examples and rehearse them before the interview. In that way you can be more relaxed and confident.
The links below take you to a more detailed guide on preparing for interviews