You should be able to form simple sentences and you should be familiar with basic grammar rules (e. g. tenses). The rest is exercise and the courage to speak. Forget your shyness! I don't think this is going to be a problem as we are easy-going people who have a lot of fun in learning by doing. Für Lernende mit Vorkenntnissen der Stufe B2/C1. Lehrbuch: In conversation B2/C1, 2nd edition, ISBN 975-3-12-501260-9, Klett Verlag, ab Lektion 12