This article on metadata and taxonomy are pretty good and well wrote a quick read.
I like how it offers the link to Leala Abbott’s article on controlled vocabulary. To top it off they used a cat picture to illustrate taxonomy you can’t go wrong.
Also PicturePark hosted a webinar “Metadata Myths and Madness!” by John Horodysk
Although the sound quality goes in and out a bit the content is very good it’s worth a watch if you a hour to kill. Check it out on youtube here.