Hi Helen,
I too was confused by some of the other posters who seem to think that preparing for an interview is in some way cheating?!?
Anyway, my view is that it's best to think of about 5 or 6 little stories from your past of situations / decisions you've been in. Each situation should be an example of various things. For example, one of your stories might cover when you "influenced others", and "leadership" and another story might cover "when you worked effectively as part of a team" and "had to come up with an original solution to a problem".
Obviously, there would be some overlap as some stories would cover some of the same things, but that's good because you may use one of the stories to illustrate one strength and then you won't be able to use that same story again in the interview.
Try to describe succintly: what the situation was, what you did, what the outcome was / relate it to what they are asking about.
Just to get you started here are a few possible questions:
Tell us of a time when:
You have dealt with confrontation
You have worked as part of a team
You have thought "outside the box"
You could have done something better
You made a mistake
You have communicated effectively
You have worked hard to achieve something
You have led a team
You have motivated others
You have thought on your feet
You have worked to a deadline
You have shown empathy for others
Some others:
What are your strengths and weaknesses?
How would your friends describe you?
How to you cope under pressure?
How do you influence others?
Any questions of a negative slant, ie "tell us about when you made a mistake" should be framed in a positive light: ie "so I learnt from that to do things a different way and now I am better for it" sort of thing. It is also probably best if these are not aviation related!
I hope this has been of some help, good luck!