There are many ways to nail a case, so my focus will always be to nuance your natural approach rather than teach you something brand new. Consultancies aren't looking for robot's, and it's really important that your personality and style shines through. The key elements of any case interview are stucturing it well, proving your arithmetic is up to scratch, and communicating your findings effectively. These will be the area's I focus most of my time on (dependant on your personal preference)
Beyond cases I am able to help you develop good stories for personal experience interviews, which are an important element of the McKinsey interview process
When I interviewed in 2014 in London I was fortunate to secure offers with McKinsey, BCG, Oliver Wyman, and a number of boutique consultancies. My experience interviewing across multiple firms allows me to share some of the nuances and adapt my approach according to your preference