How do you determine what is a good tag for a thread or video?


Active member
Up until this point I had been letting my members tag there own threads which I now regret. Most tags are not related to the thread (potty words) or are very vague one word tags.
Is it better to have a lot of tags on a thread or video even if they are vague and don't really give a lot of info about what the thread contains, words like robbed, bus, coffee, etc, or is it better to have a couple of tags per item that are more descriptive. I don't really have a clear understanding of how tags are used by search engines, I know I see the bots looking at tags a lot but I never really see people looking at them (possibly because the tags I had were basically useless. How important are tags to search results?