I can tell you about my own experience at learning vocabulary and grammar by reading a novel in English, my students’ and my target language.
You know, sometimes I read more quickly and without stopping to look up a new word in the dictionary. Then I read for pleasure. But other times I look up a word that may be blocking the meaning and my understanding the sequence of the plot.
I mean, I can’t tell you something exclusive I do when reading the novel. At different times I do different things, but the average result is positive, I’d say.
Sometimes the main point is enjoying reading the novel, some other times I focus more on grammar and vocab.
Something also nice I could tell you is that I also learn or acquire words inadvertently. I mean, I may be devouring pages – more or less – and I can say I’m acquiring words: I use them at other times when they come up to mind in an unaware way: I just can use them because they pop up to mind.
I guess reading fiction – also non-fiction – is okay for learning a language. It’s not the only thing you can carry out anyway: you should do other things: listening, speaking, writing. / Photo from: airportsporting com. Once again the picture is an illustration, but anyway it might show something from the plot from some interesting novel.