I was successful in promotion in the civil service through this process recently. As above they need to know the competency framework and then relate that to things they have done which demonstrate the required competency for the role.
They will need specific examples and must focus on what they did and the positive result at the end. It is tempting to embellish a bit but if the interviewer is decent they will probe and test their examples.
Good luck to your friend, the endless tea breaks and gold plated pension await !!!