I almost always prepare in some way. Usually I mostly write things down during the week that I might want to talk about. The day before my session I go through the notes and see what still bothers me or what I'd still like to bring up. At that time I also rank all the topics by how important they are to me and then think about how I will more or less start the conversation. This way I usually manage to cover everything and feel satisfied with what we talked about.