No writing is wasted. Did you know that sourdough from San Francisco is leavened partly by a bacteria called lactobacillus sanfrancisensis? It is native to the soil there, and does not do well elsewhere. But any kitchen can become an ecosystem. If you bake a lot, your kitchen will become a happy home to wild yeasts, and all your bread will taste better. Even a failed loaf is not wasted. Likewise, cheese makers wash the dairy floor with whey. Tomato gardeners compost with rotten tomatoes. No writing is wasted: the words you can't put in your book can wash the floor, live in the soil, lurk around in the air. They will make the next words better.
.. The Book is more important than your plans for it. You have to go with what works for The Book ~ if your ideas appear hollow or forced when they are put on paper, chop them, erase them, pulverise them and start again. Don't whine when things are not going your way, because they are going the right way for The Book, which is more important. The show must go on, and so must The Book.
I don't think anybody can teach anybody anything. I think that you learn it, but the young writer that is as I say demon-driven and wants to learn and has got to write, he don't know why, he will learn from almost any source that he finds. He will learn from older people who are not writers, he will learn from writers, but he learns it -- you can't teach it.
Becoming a writer is about becoming conscious. When you're conscious and writing from a place of insight and simplicity and real caring about the truth, you have the ability to throw the lights on for your reader. He or she will recognize his or her life and truth in what you say, in the pictures you have painted, and this decreases the terrible sense of isolation that we have all had too much of.