Therapy works best when there is a genuine desire for change. You don't have to feel "ready" in every sense, but you do need to be willing to look inward, question familiar patterns, and take an active role in the therapeutic process. This being said, it would not be honest for me to pretend that everything is under control: therapy is THE place where control is no longer needed. In fact, the therapist herself does not necessarily know what she will say next. 

But that's just exactly what makes healing so real.