When you copy YouTube tags from popular videos, they help you appear in Suggested Videos right next to those videos with million views. Thus, it is suggested that you put your primary keyword as your first tag. And then add YouTube tags in the order from more to less relevant. If your primary keyword is “cooking recipes” make sure it goes first, and then other similar word combinations like “cooking recipes for beginners”, “food recipes for dinner”, simple cooking recipes for dinner”. Best practices of YouTube tags involve using a mixture of broad and focused YouTube tags.
Choosing popular YouTube tags as your primary tags, you are not only telling the algorithm you have similar content, but letting users discover a string of relevant videos from around YouTube. If the tags for YouTube videos are chosen right and your videos show up next to popular videos in the niche your videos are likely to score a few hundreds of views organically. Yet no stuffing has ever helped. Keep the number of YouTube tags under 15 to stay on-topic.