The length is related to your story and additional questions your interviewer may ask.
The story about yourself should be 13-15 sentences.
For the PEI story I recommend the following:
- In Situation, you should briefly provide the context, usually in 1 or 2 sentences
- Task usually includes 2 or 3 sentences describing the problem and your objective.
- Then you provide a list of specific actions you took to achieve the goal. It should take 1 or 2 sentences per action (Usually 3-4 actions). Note that the interviewer can stop you any minute and ask for more details.
- The results part should have 1 or 2 sentences describing the outcomes. This part is finalizing your story - make sure it can impress the interviewer and stay in the memory.
It is important that the Interviewers will drill down into your story to understand the dynamics, your reactions and decisions and most of all the rationale behind them. They will follow up with other questions as you tell your story to make sure they understand it in enough detail. I recommend preparing for these additional questions in advance.
At the end of the interview, you will also have an opportunity to ask your questions to the interviewer. This should include 3-4 questions. Most of the candidates disregard this part in preparation, while it is a great chance to demonstrate the intellectual capacity and build some relationship with the interviewer.
The main objective is to have a good conversation and highlight your intellectual capacity and curiosity. Thus:
It is ok to ask:
- Questions that cause positive emotions and highlight consulting pros (e.g. Mck people)
- Questions on the topics you are excited about (e.g. data science)
- Non-business questions (e.g. team retreats)
It's not ok to ask:
- Questions that can cause negative emotions (e.g. work hours)
- Information you should learn before the interview (e.g. typical career path)
- Questions that may show that you are unfamiliar with consulting work (Like are you specialized in strategy or operations?)
Be prepared and good luck!