This could be a handy extension to add in to your process.
It's a fairly straight forward tool - when viewing any YouTube video, tap on the Tag Snag icon and it will come up with a listing of the tags the creator has used for that clip, as shown above.
In addition to this, Tag Snag also enables you to extract the tags from multiple YouTube videos at once. If you conduct a search, then use Tag Snag in the results screen (with the 'Multiple Videos' option checked), it will display a listing of all the tags used for those videos
The list could help you create a more effective collection of tags to include in your own YouTube uploads, based on what the most popular videos in the same niche are using.
Tag Snag isn't the first tool to provide this capacity, and there are various ways in which you can extract the video tags on YouTube via the HTML code. But the extension makes it easy, and as noted, it could be a good compliment to your YouTube SEO process.
You can download Tag Snag from its Product Hunt listing here.