Set your primary target keyword as the first tag

A study of 1.3 million YouTube videos found a small relationship between rankings and the presence of the keyword in the video’s tags. Some also believe that YouTube pays the most attention to your first tag. Whether this is true is anyone’s guess. But given that YouTube’s official guidance for tags is to “use the words and phrases that make the most sense for your video,” your target keyword is a good starting point. So it’s advisable almost always use your primary keyword as your first tag.