Writing instruction is important. It shouldn’t be divorced from reading, but it can help a writer make sense of what it is they’re seeing.
For example, when reading two books, a reader can point to the one he enjoyed, the one that evoked emotion, the one he thought about for days afterward. But a writer needs more. A writer needs to ask, How did the author make the story enjoyable? How did he evoke emotion? What did he do to make the story or characters memorable?
The three writing books that are at the top of my list are Writing the Breakout Novel by Donald Maass, Description by Monica Wood, and Stein on Writing by Sol Stein.