This post linked from Mad Genius Club is a few years old, but for an SEO noob like myself, it’s a good way to start.

I have my doubts about ever mastering it, but I won’t get any better just sitting here.

For Example, War To The Knife (Laredo War Trilogy Book 1)‘s main categories are:
FICTION > Science Fiction > Space Opera
FICTION > Science Fiction > Military

However, it’s present in all the following categories:

Books > Literature & Fiction
Books > Science Fiction & Fantasy > Science Fiction > Adventure
Books > Science Fiction & Fantasy > Science Fiction > Military
Books > Science Fiction & Fantasy > Science Fiction > Space Opera
Kindle Store > Kindle eBooks > Science Fiction & Fantasy > Science Fiction > Colonization
Kindle Store > Kindle eBooks > Science Fiction & Fantasy > Science Fiction > Galactic Empire
Kindle Store > Kindle eBooks > Science Fiction & Fantasy > Science Fiction > Military > Space Fleet
Kindle Store > Kindle eBooks > Science Fiction & Fantasy > Science Fiction > Military > Space Marine
Kindle Store > Kindle eBooks > Science Fiction & Fantasy > Science Fiction > Space Opera

We did that by putting in the following keywords: “Fleet, Marine, Space, Action, republic, Colonization, Starship”