Sometimes the simple tools work best. Consider, if you will, the humble index card and all the ways it can help you write a better book.
Capture ideas on index cards
Index cards are one of my preferred ways to capture ideas. They are decidedly low tech. All you need to capture ideas with them are some blank index cards, something to write on them with, and a pocket to put them in.
Those humble index cards work when it’s best to stay silent. They’ll work if you have an insight while standing in line at the supermarket or listening to a sermon in church.
Use index cards to get an idea of how your ideas relate to each other
Once you put ideas or insights on index cards, you can easily arrange them in a variety of ways to learn how your ideas relate to each other. I like spreading them out on top of the bed, on the floor of my writing cave, or on a large artist’s clipboard. When I notice things that seem to relate to each other, I put the cards near each other.
Plan your book using index cards
Put a phrase representing each of the key ideas or stories for you book on a single index card. Keep re-arranging them until you get an order that makes sense. Then do the same thing with the key points and examples in each chapter.
Some technical details
I like plain white 3 by 5 inch index cards. They fit in your pocket and you can write or draw on them easily.
I suggest one pocket for blank cards and another for cards you’ve used. If you really like using index cards you may want to consider a Levenger “shirt pocket briefcase.” I’ve been using mine for over thirty years.