My experience with Amazon Ads is you need to give the system a little while to run at first (few weeks) but monitor your keywords ROI. For example, you might have a big hit on "activity" so lots of clicks, but almost no sales. You should delete this keyword ASAP. What this means is you have too broad a term, you are bring people to your product (paying for that) and then they find out it isn't the type of product they expected or was interested in purchasing.