When uploading a video to YouTube, it’s critical to get the right keywords and tags in place. No matter how clever Google’s technology may be, it’s nowhere near understanding a video yet. The most important part of being found lies in the words with which we surround the video.
The keywords that you need to have in place in your title and description can be researched through the normal channels, just as with conventional SEO: have a play with Google’s own autocomplete, your own Search Console data, or tools such as Keyword Planner. Don’t skimp on the description; YouTube allows you plenty of words, so use the facility.
Tags are a bit different: if the keywords make sense as tags, then of course use them, but you might also like to investigate what existing highly-performing videos are using as their tags. If you install the free Tags For YouTube Chrome extension, the tags for a video will be shown at the end of the description. You may well be surprised at how many tags are included with top-ranking videos.