Once you have been accepted onto a CELTA course, your provider will give you a list of recommended reading. To be honest, while I bought some of the books, without context I couldn't really relate to what I was reading.
I definitely don't think the little pre-course reading I did had any bearing on my final grade. As I said in my previous post, there were three things that I felt helped me, the most important of which was taking all criticism on board and making a concerted effort to address it in my next observed lesson.
Of course this is just my opinion - others will undoubtedly have different advice/thoughts. If you have Facebook, I would recommend joining the CELTA group (https://www.facebook.com/groups/3925889087/
) and chatting to people there.