Chris Aldrich points to this open text, How to Make Notes and Write, by Dan Allosso and S. F. Allosso. In  a nutshell, the book describes how to take notes from readings and sources, find how they are connected, and weave the results into longer works. This is sometimes called personal knowledge management (PKM) or the Zettelkasten method. Aldrich offers a link to an annotated version of the book. I find the approach a bit mechanical (as maybe it should be if you’re just learning). Then, I have virtually zero desire to write longer works, and prefer to be able to envision the entire text in my own mind before writing it and filling it in.