Mastering the case is one thing. However, before that there are
- Resume and cover letter screening
- Aptitude tests
Once you passed these, you will have to do cases + the personal fit part. Now, the importance of the personal fit part varies across firms. For instance, McKinsey places equal weight on the PEI and the case. If you fail one or the other, you will not get an offer. So make sure to prepare it properly with someone who knows what is needed here (types of content and ways of communication)
Having said that, the case is definitely the most difficult aspect of the whole journey...