Here are some thoughts/advice on it. I’m not sure any one cares about my opinions on this matter, but I thought I’d share it anyways.

1. I dislike over-tagging (I’ve fallen into it myself at times). Of course how many tags are too many is a subjective thing. In my mind, when you start having books that having 10 tags per book or start having a list of tags that is so long that it is painful to navigate, you are probably over-tagging. And, yes, if you have a tag called “british-literature-from-the-first-quarter-of-the-19th-century”, you are over-tagging.

2. Basically, in selecting what tags to add and what tags not to add, as much as I can, I try to to think about what will be most useful. Generally speaking, tags are only useful in so far much as they group multiple books together, so if you are adding tons of tags which only have one or two book associated with them, you get a high amount of tag-overload with a low amount of benefit, because they aren’t even really grouping similar books together. So when you create new tag and add it to a book, think about it, is this tag actually going to be used for other books? Think general enough to contain at least 4 or 5 books in your library (either concretely or potentially in the future), but specific enough where it does exclude some books. I sort of break my own rules here with fiction (which is one of those “blob” tags, but I find it useful for some purposes).

3. Think about repetition too.  In my personal opinion, tags which conceptually contain other tags should sometimes be eliminated (ie. you don’t need “history” but you probably should use “british-history” and “american-history”), but in other cases it makes more sense to use the ‘parent’ tag and the child concepts (ie. have a general “theology” tag but then also keep “eschatology” and “ecclesiology”, or having a general “technology” tag but also having “programming” and “web design”). This may seem inconsistent, but basically my thought is that I would rarely look for a book in “history” (that is prohibitively unspecific) but I would sometimes look for a general “theology” book.

4. Tags are generally for subjects and not authors or people (a potential exception would be a very famous historical figure that a lot of people write about (say ‘luther’, ‘churchill’, ‘plato’ or ‘hitler’).

5. Any tag that is a phrase of 4 words is probably getting too specific.

6. Consistency helps!

7. Every book gets at least one tag (so it can be found without searching for the name or browsing the whole list)

7. Trying to consciously limit the tags per book to 3 or 4 or 5 and average it at 2-3 will ensure a good balance between specificity/generality and usually makes for an interesting and helpful amount of tagging.

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