Go back through your logbook. Try to remember the times you:
--Screwed something up or made an error in judgement. What happened and how did you deal with it?
--Had a conflict with a crewmember, superior, or subordinate.
--Failed a checkride. What happened, what did you learn, did you agree with the check pilot?
--Diverted to another field. What circumstances?
--Had an emergency situation. What circumstances?
--Used crew resource management. Ever had your mind changed by the crew? Ever had to make a "team" decision inflight? Ever had to try to convince the Captain to do something different?
--Broke a rule on purpose. What circumstances would make you do this?
Don't "over-prepare." They aren't going to want to hear the same answer some guy from your company or squadron gave them two weeks ago, and they aren't going to want to feel like you've memorized some monologue about your stories. Think about the situation and what points you think are important, and then move on to the next one. You can use the same situation to answer more than one question, and you can use the same situation with more than one of the interview team.
They're probably going to ask you about failed checkrides, but they are doing this to see how you handled it and what you learned, not to compare you to someone who hasn't failed one. Their approach seems to be that it's happened to everyone, and your attitude about it is more important than the fact that it happened.
They're also going to ask why you want to work there, and why you're a good "fit." If you haven't read "Nuts," read it. It's a good read, and you'll learn some things about the way the company "ticks." If you can't find some things you like in there, it may NOT be the place for you, but I think most guys will find enough things that appeal to them that you can come up with a good sincere answer about what you like and why you'd be a good addition.
Don't get nervous about it at all. If an interview can be "fun," this one is. It's totally non-adversarial, and you shouldn't feel like you're having to "prove your worth." Know your record, your strengths, and your weaknesses, and just act like a "normal person."