I've applied before, after I was let go from a Big4 firm. Can I ask, which firm did you train at, your schooling background and why were you let go?

Asking because Big4 firms tend you scrutinise your CV, and if they don't like what they see they may not consider your application.

Assuming you get an interview, the interviewing partner will also tend to ask you a series of technical questions on corporate work, or ask you to analyse a case study. The answers to these questions will not be found in your textbooks, so it would be best if you have working knowledge of corporate work.