When all else fails, use your head bone. Reading teaches you how sentences and paragraphs are built. As you go along you will learn more complex things I will not call rules, but customs. All of these things provide you with that most important thing, the absolute and undivided attention of the reader, one who does not half-read a paragraph while thinking what a dumb mistake you made in the last one. His mind is ready to receive.
Writing improves with practice and comparisons to good writing.
No one actually teaches you to write. All anyone else can do for you is file off some of the rough edges. Because writing is a whole life experience that involves your total personality, culture, and physical makeup. He is a very fast runner. I often tell him that he should run.