Right tag words can mean the difference between many CM dollars (CM$s) and no CM dollars for you.
You get CM$s in proportion to the number of visitors your stories attract; so, high traffic means high dollars for you. And you increase the traffic propensity of your stories by providing better keywords.
For just the right tag words, think like a reader searching for a news; what specific words, phrases, or groups of words would he be thinking of to feed in the search engines? If you were to categorise the news/article/feature, which specific category will you slot it in? Think specific categories, not general.
As an example, here’s a link for you: http://www.thejourneyer.com/feature/20110201/rana_will_be_action_entertainerravikumar-32135.html. This TJ news has the following tag words: A. R. Rahman, action drama, celebrities, news, Ocher Studios Private Limited, Rajinikanth, Rana, Ravikumar, Robot, Soundarya, triple role. The right (specific) tag words/phrases would be Rajnikanth triple role, Rajnikanth robot, Rajnikanth action drama, and Rajnikanth Soundarya, and NOT Rajnikanth, celebrities, etc., which are very general categories.
So when thinking of tag words, don’t generalize. Specify.
Second, while thinking of specific phrases and words, make sure your tag words are like computer folders, in one sense. If you’re not going to put any more files in it, there’s no point having that folder. So don’t make a folder (read use a tag word/phrase) if it only has one file (read if you cannot categorise another news/article/feature under that tag word/phrase).
So, use appropriate, relevant, and well-thought tag words (based on the two ideas above), as opposed to adding them on carelessly. Providing meaningful tag words will only increase traffic (and your CM$s) to your news.
You can use as many tag words as possible, long as they all are meaningful.
Cosmos Writers Editorial Team