My very first publication was a book review. Book reviews can be very helpful at the beginning of your academic career. I reviewed for a weird semi-academic journal that only had reviews of foreign books, and I was their Scandinavian reviewer. That's how I learned to read Norwegian and Danish, that I have actually never studied. The journal was bi-monthly, and I contributed to every issue, only it was against the rules to have more than one review in the same issue so all reviewers had lots of pseudonyms. I would, for instance, use my father's or my grandfather's first names as pseudonyms. Once a year, there was a special issue on children's literature, and I always reviewed several books for those. I reviewed Tove Jansson's Moominvalley in November when it first came out. Now mind, this was behind the Iron Curtain, and reviewing was the only way for me to get hold of books. And of course I wasn't allowed to keep them, they went to the library.
Occasionally, I reviewed something for the journal on children's literature. I am quite proud of having reviewed the first Russian translation of The Lion, the Witch and the Wardrobe.
Some years after I had come to Sweden, a new journal in children's literature started, Opsis Kalopsis, and I happened to sit next to the editor-in-chief at a reception, just as she was looking for reviewers. I wrote for this journal for many years (and was allowed to keep books). I mostly specialised in fantasy and had “my” authors, including Lloyd Alexander, Diana Wynne Jones and Philip Pullman. Many reviews fed into my academic writing.
For a while I reviewed books for the cultural journal of the Swedish church. I did it because these were not children's books, and I thought it might be useful to add to my cv. I reviewed such authors as Harold Bloom and Alexander Solzhenitsyn. I have written reviews for Scandinavica, and occasional reviews here and there. I don't review on a regular basis any more, but every now and I am asked to review a professional publication. I only do it if I am really interested, which I most often am (I guess that why they ask me).
Looking back, I think that reviewing was an extremely helpful writing practice. Staying within word count and keeping deadlines is always good training. Following an author for several years was stimulating and resulted in author portraits and other publications. And in many cases, the journals I reviewed for would eventually take my own article.