We all learn by imitating. The simplest way for you to learn about writing reviews is to examine what other reviewers are doing--and I don't mean dinosaurs like Samuel Johnson. You ought to simplify your problem by selecting one of the three genres you name in your question. Take book reviews because they are the most plentiful. The best place to read book reviews--by far--is in the Sunday issue of the New York Times (which is easy to find at many public and school libraries). Just observe what the other reviewers are including in their pieces and what sort of format they typically follow.
The New York Times also gives extensive coverage to movies, and their reviews provide a lot of useful factual details, such as the names of all the cast members and the names of the characters they play. Another good source of movie reviews is Weekly Variety, which is available in the periodicals room at big public libraries and colllege libraries. You ought to familiarize yourself with these two powerful publications if you are going to be involved with reviewing or any other aspect of show biz.
What you include in a review will depend a great deal on how many words you intend to write. Your own opinion of the work is probably the least important and can be expressed in one or two sentences at the end. The reader wants to know who, what, where, when--that sort of information. But you can see what the other reviewers--your colleagues in the profession--are doing and do the same.
Other good sources of book reviews and movie reviews are Magill's Literary Annual and Magill's Cinema Annual. Both sets are available in the reference department at good libraries. Just ask at the reference desk.