In general, one-work authors should be tagged under the author's name (in the format described in this post). If the work is a TV series (where there are many authors, typically unknown), under the series name as discussed earlier.
If the single work is a single novel (e.g. a new author), then we don't need a tag for the work, because we'll end up with a huge number of these tags. Fans of the work can follow the author tag (and get the added benefit of seeing when the author does release something new - it is likely that they will be fans of that as well). If someone's trying to find questions about the work and doesn't search for the author, then the search ought to find the work title in the question.
In the case where the "single work" is a series, there is perhaps value in a series tag, although this is more the case when the work is particularly well known (as with harry-potter, or twilight).
If a tag is missing from a question, then anyone can edit that to add it in, and the change doesn't even need approval for most users, since the required rep is low. (If the tag is new, then some users cannot suggest this edit, but they can flag or bring it up in meta or chat, and in most of the cases this is relevant to, the tag will already exist).
There may be some questions that are about the author and not the work (e.g. questions about fandom are on-topic) or about the work and not the author (e.g. questions about fan-fic). In those cases only a single tag is appropriate - it seems likely that the former would be much more common than the latter (i.e. author is preferable over series). The tag wikis help explain the difference, although hopefully people would guess correctly in these cases.