Bidding on the right keywords for less, encouraging more positive reviews to attract new shoppers, making campaign tweaks based on perceived target audience trends, and otherwise can lower your ACoS, but any optimizations need to be handled with care. Even seasoned Amazon advertising veterans make mistakes as shoppers can be difficult to keep up with. Doing things solo, especially if managing multiple campaigns, can be a nightmare in this sense. It also heightens the risk as you may end up applying guesswork and experimenting. 

Your best bet is to use an automated tool that handles all of this carefully, making informed tweaks by using AI to analyze your campaign, listing and target audience data. Tools like Trellis offer huge benefits including intelligent keyword bidding, report generation to provide you with valuable performance insights, substantial cost savings and maximum profit potential, and the ability to rank higher while drawing more customers who are likelier to convert.