Stan Prokopenko is a great teacher, who has produced videos that are so cool in how they use animation to reinforce the excellent narration. He has built a platform for other teachers too, introducing me to some other great teachers, including some of his contemporaries Dorian Iten and Aaron Westerberg, as well as some classics Andrew Loomis and Anders Zorn.
I learned a lot of the basics from Prokopenko, including the Loomis method in his course Portrait Drawing Fundamentals.
Westerberg is so generous in showing some of the nitty gritty of how he paints in his course on Proko.com: Portrait Painting in Oil.
I especially love the preparatory phases where he is treating the surface for painting; photographing and working with his model; and experimenting with photoshop and small color studies.
He also works with the limited Zorn palette and has a great blog about expanding the Zorn palette.
Another nuts-and-bolts teacher, Iten has a great course on Proko.com: Drawing Fundamentals: Accuracy, Values, & Light.
I also found his website to have a lot of these ideas explained as well (especially his articles on Accuracy and Value Studies).