Like bowlturner said, there is, generally speaking, no need to get any sort of pre-approval on tags. If you think it will be useful, add it and see if it takes off. That's what the create tags privilege is all about; at a certain amount of reputation, you are considered to know the ways of the site well enough to recognize when a new tag might be more appropriate than any existing tag.
However, do be careful about meta tags. Those are tags that don't directly help categorize what the question is asking about. Meta tags should probably be discussed on meta beforehand, allowing time for a clear community opinion if perhaps not consensus to form, and should be added very sparingly.