Your preparation should have three parts, industry and company background, role specific questions/personal motive and interview skills. There are abundant of information available on the internet. You should also think hard about why do you want the job. What do you want to do on a daily basis while you are with Deloitte? Does it match with your ambition/personality? Why this role/ why this department? Why this firm?
As per the interview skill section I would recommend the STAR framework.
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