I suspect your friend is quite correct in saying that a number of people joining the college didn't know very much about ATC. That's kind of the point of the college !
As Gonzo, among others, has said a number of times the point of the interview process is to pick out those who have the
right core skills to be able to be trained as ATCOs. If you already knew everything about ATC we wouldn't need a college we could just give you a headset and send you to a unit.
As for what the core skills are there are masses of clues all through this and other threads but the key (as with any interview process) is to be yourself and allow us to worry about the criteria. Our Interviewers (well most of them anyway) are good at choosing those that match up and if you try to be someone you're not you'll usually be caught out. Worse still you might get away with it and end up with a short unhappy career in ATC.
