If you haven't already, look at the competency descriptors, and the SPA competencies to get an idea of how to structure it.
Follow the STAR method the best you can, and really put an emphasis on what you actually did (I did this, I thought this) the examples you give don't need to seem like you're saving the world, they just want someone who can directly answer the question - stick to the competency and said how you did it/what action you took.
I was asked 6 questions total relating to, Personal Awareness, Personal Effectiveness, Team Working, Respect for Diversity (study the 9 diversity points on the website), Service Delivery and the Job Knowledge (What is the national policing plan for 17/18, and the training schedule, I listed the 4 modules and what they involved).
I passed the interview, but got caught off guard with the questions that I was asked, so have a couple of examples for each. It's difficult but try not to follow a script too much, at times I felt like a robot trying to get my answer out (which they noticed)
Hope this helps anyway.