Preparation always helps.
Apart from the obvious differences, most consulting firms follow a similar recruiting process and there is plenty of resources online (just google case study) that will give you an idea of what to expect.
However, at the end of the day, you either have it or you don't, so do some research about the firm, be ready to explain why you want to join Deloitte, and take it easy.
Also, important that you try to enjoy yourself. It may sound stupid, but people want to see whether you would like doing what Deloitte does (...) and whether they would like to work with you.
And do not ask stupid questions.