Regardless of your qualifications, state that you are very well qualified for the position.
Here you have to come up with something or you strain credibility. Make it small, well intentioned mistake with a positive lesson learned. An example would be working too far ahead of colleagues on a project and thus throwing coordination off.
Don't get trivial or negative. Safe areas are few but can include: not enough of a challenge. You were laid off in a reduction company did not win a contract, which would have given you more responsibility.
First, if you have experience that the interviewer does not know about, bring that up: then, point out (if true) that you are a hard working quick learner.
Pick a specific incident. Concentrate on your problem solving technique and not the dispute you settled.
Be sure that you refer to something that was beyond your control. Show acceptance and no negative feelings.
Talk about having fun by accomplishing something for the organization.
Speak about specifics that relate to the position you are applying for. If you do not have specific experience, get as close as you can.
If you have not, say no. If you have, be honest, brief and avoid saying negative things about the people or organization involved.
Have a good one ready. Be sure and use a suggestion that was accepted and was then considered successful. One related to the type of work applied for is a real plus.