I have long since stopped getting Amazon sales at all for any of my books, except when I run countdown deals or do something else notable, and I haven't done anything notable in a long time due to focusing on other things.

I suspect I need to pay more attention to my keywords. Back when I was publishing I just shrugged and filled out Amazon's seven keyword slots with various elements that feature in the stories, since I couldn't come up with anything specific.

For instance, one of my fantasy novels has this: Warrior woman, coming of age,supernatural, sorcery, fantasy heroine, sword, action.

One of my space opera novels has this: Space opera, epic, war, strong femaleprotagonist, adventure, anthology, action adventure.

Looking at it all now, this doesn't feel very impressive. All of these feature in thousands of other novels. But how precise can I be when I'm choosing keywords, before I'm putting in something so specific no one is ever going to search for it? I don't really search Amazon by keywords so I don't know how people do it. Is there a way to see which keywords are currently popular?

Should I put in whole sentences, like "female mentor and student relationship" or just one or two words?