I'm still relearning everything I used to use to paint back before I started doing it on computers (a mistake, in my opinion and hindsight).
I've been reading this thread recently and I've found that I already use some of the techniques (underpaininting with glazes on top to achieve certain effects, etc.), but I'm rediscovering some things I'd forgotten, and am learning some things that the Commercial Art school (yeah, I know, I know) never taught me. I wish I'd found this thread about a year ago...