I currently work in a PRU, and my main advice is always be flexible but consistent. Make sure there is always a carrot so to speak such as a chance to play games at the end of the session. We have 45 minute sessions, around 35 minutes work and 10 minutes games. I think what you will quickly discover is that advice tends to contradict itself. After saying being flexible you still have to have that line so they know the boundaries. A key thing I try and teach students is the ability to negotiate. If they dont want to do a piece of work thats fine as long as they can come up with an alternative. So in summing up flexibility, but clear boundaries, a carrot to end the lesson, rely on your gut instinct when dealing with incidents oh and most importantly a sense of humour to go with those broad shoulders you are going to need.