Start with his generic support guide found here.
From there, just try to catch his stream while he's on. I'm not sure how good he is at commentating his actual stream, but even if he doesn't do it all that well, just watch what he does. Where he wards and when, etc.
I believe that he has a guide written for each individual champion in addition to his generic guide, which can all be found on solomid.
Another tip, is try to play quite a bit of ADC as well. It gives you quite a feel for supporting, because you learn, as an ADC, what you like your supports to do, and then you can approach the role of support from the mindset of "if I were an ADC, I would want my support to do <insert action here> right about now".