Many students purchase books and use the endless resources on the internet to help them prepare for their exams. That is great, and I definitely recommend reading anything you can about the exam, but that method doesn’t include speaking practice. You can read all about the speaking section, possible question topics and example answers, but that is all passive learning.
If you really want to be ready for the speaking portion of the exam, you need to actually practice speaking. Speaking by yourself in the mirror is a great way to get comfortable for the speaking section, but the mirror doesn’t make corrections and give you feedback.