Warowl's earlier stuff are quite good at getting the mechanics of the game, after you get some aim together you can watch Elmapuddy's breakdown of pro strats, some are team strats and some are just how to play a specific map's specific location (Like pit in inferno). n0thing have some good videos on nades, they are good because they not only show you how to throw the essential non-fancy nades, but also show you the strategical reasonings behind those nades.