Here is another really excellent downwind instructional video by Jeremy Riggs in conjunction with Justin Gordon from Sugar Ranch Maui. Check out all of Jeremy's vids at his website http://paddlewithriggs.com/ and while you're looking around the Sugar Ranch Maui looks like da kine place to stay on Maui.
Justin is riding a rudder equipped SIC which makes turning the board much easier than a board without a rudder. That said, rudders add quite a bit of cost to the board and the lack of rake in the rudder fins makes them difficult to use in kelpy waters like we have locally. Some of the instructional tips Jeremy gives Justin in this video are rudder related, but the bulk of the info can be used on any board, making this one of the best instructional vids I've ever seen.