Tags help users find your video when they search the site. When users type keywords related to your tags your video will appear in their search results.
YouTube does consider user engagement as well (like number of views, views in common and user “retention”) but tagging is the *first* step to ranking your video in YouTube search results (and thus getting a good chance to get ranked in Universal Results as well).
A most scientific (but still useful to start brainstorming) approach to classifying YouTube tags (pdf) groups all the tags as follows:
- Generic relationship between tag and video content:
- Tag identifies what the video is of at its most primary and objective level – no subject specific knowledge is needed to make this distinction (e.g. a video of a cat, tagged as ‘cat’ or ‘animal’)
- General YouTube defined Category or Genre (e.g. Comedy, Entertainment, Music)
- Specific relationship between tag and video content:
- Tag identifies what video is of. Familiarity or some existing knowledge is needed to make this connection (this may be about names, locations, venues, etc).
- Tag only useful to a minority of users, specific individual or group
- Refining tag (Tag which cannot stand alone – only useful when looked at as part of the larger tag set (e.g., episodes of a series of videos specified by a number)
- Self-reference tagging (e.g. “my dog”),
- Irrelevant/Non Useful Tags (those may vary from attention-grabbing and misspelled tags to conjunctions and prepositions).