Here are my 5 tips:
1) Practice mental calculation daily (percentages, decimal places, large numbers, arithmetic) – even though it's not the most important part of the interview and it's allowed to make mistakes, you need to master your numbers very comfortably. If you don't, during the interview you will start feeling nervous and will perform worse on other things. I was doing at least 30 min a day of mental arithmetic for several months (download one of the apps on your phone, there are plenty).
2) Cases, cases, cases – do as many as you can. After you gather a bit of experience of practicing with your fellow students, try to find a person who is now working or has worked in the past at the MBB's recruting and ask them to simulate an interview with you.
3) Prepare and practice personal fit interviews – they are as important as the cases. Write down your stories, practice telling them with your fellow students, or with an expert.
4) Beware of your mental state – try not to stress too much before and during the interview (I know it's easier said than done). Do sports, take care of your health, try yoga, meditation – whatever makes you less stressed. I've seen so many candidates pale as a sheet of paper during my time as an interviewer at McKinsey, all worried and jittery – as you can imagine this doesn't help your performance.
5) If you get rejected, it's not the end of the world, do prepare yourself mentally for this thought! A close friend of mine became depressed for months after being rejected at McKinsey. I think it was because she treated this as a "do or die" situation. Do not do that! There are infinite options of different careers and adventures out there, you don't need to become a strategy consultant to be happy. Just try to embrace this before going into the interview room – and you will be better prepared for both failure and success.