I've just completed Level Three of the Free Association's Improvisation course, where I learned a performance structure called the 'Harold'. Our improv class teams had our graduation show last night - which was a very daunting prospect - and it proved to be one of the most rewarding experiences I've ever had performing.
I can't recommend this course enough, it's been such a wonderful place to learn so many new skills, make new friends and join a fantastic and rapidly expanding community. The teachers are incredible at what they do and you always feel 100% supported. The perfect learning environment. I highly recommend anyone with or without previous performance experience to sign up and do this course. It helps in so many areas; listening, confidence building, learning to saying yes, supporting one another and creative stimulation.
Their website is here. Bring on Level Four!