depend on what you want to do, are you doing dynamic apnea, or finswimming on the surrface with a snorkel. Finis actually makes an instructional video, I think more for finswimming-heard it's not that usefull for freediving but might be fine for what you are looking to do. If dynamic is what you want there an article here in the taining section- also might look up the peter pederson 200m record video on youtube.
Performance Freediving | home | teaches a course out of malibu if you want to take it that far
