AMS always worked better for me than FB--though that isn't saying much.
By no means are my AMS campaigns huge successes, but I have picked up on a couple of things that might be useful (keeping in mind my relatively small dataset.
In recent times, the sponsored product ads based on product targets have performed better than sponsored product ads based on search terms in terms of actually generating sales. I used to think search-term based ads were better, but the ones I have running currently aren't doing a thing (except burning money). I don't know why that is. They didn't used to perform so differently.
Sponsored brand ads do a little, but not much. Remember all the fanfare about custom images for sponsored brand ads that made them perform so much better? My one sponsored brand ad that does much in terms of sales is an old one with no custom image. But maybe I did overkill on the images. Each one of my new sponsored brand ads has a an image carousel (you can have up to five images). Theoretically, the movement should draw the eye. But maybe it doesn't for some reason. I don't know. As I said, my dataset is rather small.
Product targets give you the option of targeting by categories or by individual products. Individual products give the further option of exact or expanded. It's okay to use expanded, but monitor carefully. That's supposed to pick up related product searches, but sometimes Amazon's idea of what constitutes related is a little...broad. You can counteract really odd hits using negative targeting using. If you use categories, narrow ones are better than really broad ones, though it's a dilemma. Fantasy all by itself gives me the most sales, but also way more clicks. Goodbye, ROI!
Keyword targets use exact, phrase, or broad targets. Stay away from the third one. If you check the actual search terms Amazon has decided to connect to your ad if you go too broad, you'll probably find some that don't fit the book at all. Phrase is better, but you may still need to use negative targeting to cut out the occasional mismatch. (For instance, "fantasy" in phrase mode can connect to "erotic fantasy.") Obviously, there's no point in that kind of connection unless our fantasy actually is erotic.
Hopefully, those observations may save you a little time.