1st - work on your 1st round feedback.
2nd - different offices have different final rounds (e.g. some BCG offices have the written cases as the final step, while others have it at the beginning)
At the final round, I would expect a bit more structured and demanding approach to the fit part. The partners in the last round are more experienced and they will challenge every single detail of your story. So make sure that you have a couple of backup stories. Thus:
1) Make sure that you've prepared everything: A story about yourself, motivational questions and the main FIT stories. Also, don't forget about your questions to the interviewer - you'd rather have an interesting conversation and score some point instead of a simple Q&A session
2) Then go through each story and think of the additional questions the interviewer may ask. It’s important since additional questions will take up to 50% of the interview. Try to remember the main details and facts and make sure that you know how to explain the key concepts quickly. Test your stories with your friends, ideally consultants, and ask for their feedback. There can be multiple groups of additional questions:
- The interviewer may be interested in details about the context
- He may want to check whether this was your effort or more sort of a team effort.
- “Have you faced any difficulties while implementing your solution?”- Typically an interviewer would like you to tell him how you’ve overcome those difficulties.
- Your interviewer will check how real your story is. You should be ready to provide even more granular actions, key milestones and a breakdown of potential effects.
3) work on 3-6 backup stories. During your interviews, you can then use these stories or adapt these stories to the additional questions your interviewer asks you.
You may be interested, why you need to prepare several stories for each question? At the end of the day, it's not that easy to come up with all of these stories. I've answered here: https://www.preplounge.com/en/consulting-forum/repating-fit-interview-stories-927#a1813
4) Next step is talking to consultants. I recommend doing a couple of mock interviews, both case+fit. You can connect with consultants via friends, company events or even LinkedIn. Consultants are entirely opened to share their experiences, but the biggest problem will be the lack of time. Sometimes you’ll need to send a kind reminder to your request, but it pays off.