I have had the TubeBuddy add-on for a while, but today I discovered that it has a feature called "tag tools". When you go to edit your tags, scroll down and hit the "suggest" button. It shows you some suggested tags that you may have missed and you can add them to your tags. I searched for a pretty simple term they suggested for one of my videos while using a browser I'm not logged in as myself and my video ranked second for that search term. I'm going to go through my videos now to update the tags.