as for your first question, the PEI at McKinsey is structured around three key dimensions, leadership, impact and drive. I have provided a description for them below:
1) Leadership is about leading a whole team in a challenging situation and showing team management skills. Questions include:
- Give me three examples of a time that you lead a group.
- What are some key lessons you have learned about motivating people?
Here you want to emphasize how you overcome a difficult situation leading a team.
2) Personal Impact is mainly based on persuading someone about doing/not doing something. Questions include:
- Tell me about a time that you persuaded your boss to go along with an idea you had.
- Tell me about a difficult situation where you had to rely on your communication skills.
Here you want to emphasize your influence on someone else, usually in disagreement with you.
3) Entrepreneurial Drive is about implementing something overcoming major difficulties. Examples include:
- What was a situation where you set a major goal and been able to achieve it?
- What has been your major accomplishment so far?
Here you want to emphasize the achievement you reached and the process that led you there.
The best way to structure your stories is to use the STARR approach (Situation, Task, Action, Rational for action and Results), which helps the interviewer to understand all the key areas of your story.
Besides the previous dimensions, common questions also include:
- Tell me about yourself
- Why consulting
- Why McKinsey
- Why should we hire you
As for your second question, yes, you should always start the case with a structure. Moreover, you should also structure your approach for questions asked during the case, before proceeding with brainstorming/creativity solutions.
Hope this helps,