You don’t need to read a book about learning to say “No” and you don’t need to read a book about learning to say “Yes”.
Saying yes to opportunities and adventures which may offer much learning is good.
Saying no to situations that are not good for you, whether directly harmful or exploiting senses of obligation or guilt, is always an option and often wise.
The rest you can imagine, and spend time with a better book!
Now that really is Self Help!