My opinion is a little different than most. Books are a fine way to get an understanding of the nuts and bolts of the various poker games. That said, the trends and tactics - game dynamics - tend to change constantly, and videos are the best way to keep up with the current game.
A good example of the latter is a couple of video series on tactics that Vanessa Selbst did a few years ago. In the first series she gave some specific advise. However, in the second series her opinion had changed, because, she hinted that the game dynamics had changed.
So, my advise is to understand the basics, and then work to keep up with the changes.