The best thing you can do is to start preparing now, before the business school. Once you are there - you'll have no time for prep.
I would work on several topics:
1) Prepare your resume in advance (just to save some time later)
2) Star preparation for the cases before b-school. It is a very broad topic, but I will give you some advice:
- Time is the King. You'll need at least a month if you can prepare full-time. 3-4 months if you can't work on it systematically
- Feedback and coaching will save you time. Work with an expert here. An expert will give you the right knowledge.
- Practice cases with the other candidates to get the skill. Try to find the candidates with at least one real MBB consulting interview experience and 50+ cases solved. Ask for the cases from the real case interviews. Unfortunately, in the beginning, you'll have to solve the "Chicken and egg" problem in finding the experienced partners
3) 2-3 weeks before your interviews (or even earlier in case of MBA) start crafting your FIT stories. More details here:
4) At school start attending all the consulting events, although I would not make too many bets on coffee chats. Here are some ideas re coffee chats:
5) Find the classmates who were working in consulting before and would recommend you to the on-campus recruiting coordinator. More on the referral here (although in your case, it will be not an official referral, but recommendations from your ex-MBB classmates will significantly increase your chances):
Best of luck!