Try this:

http://www.instructables.com/id/How-to-use-a-rotary-cutter/

this one is interesting for cutting curves:

http://craftapple.wordpress.com/2008/11/20/tutorial-cutting-curves-with-a-rotary-cutter/

A non-video...
http://www.purlbee.com/rotary-cutter-tutorial/

FW

Free video tutorial at this website http://www.wonderhowto.com/how-to/video/how-to-use-a-rotary-cutting-mat-232732/

There are others on YouTube, just search on "rotary cutting"

I have only done a beginners class for rotary cutting (ages ago) - does anybody know where I can watch a refresher on line? Thanks ! x