Either testing [SVAR, Berlitz, Versant+(Comprehension+Speech+Typing/Data Entry)] or the Initial Interview comes first. Sometimes, they combine the Initial and the Final Interview. This is usually done to process applicants faster.
After, they would ask you to review materials for the mock call. Usually, it would be about the account that you were considered for. Then you'd have the mock call. If you passed, they would give you your JO. However, if you failed [or they see you more fit for another account] you would have to review and go for a mock call again for another account.
We were told that the whole process can be done in 4 hours, but they don't put in 'One Day Application only' for nothing. I went in at 11AM, I finished at 1AM the next day due to the number of applicants and me heading out for a couple of hours to eat.
From my view point, I must wear a pleasant clothes.
I would wear a business-like clothes, touch -up a litttle, tie my hair, and always wear
a beautiful smile.