A "preview" of a story is something you write before you have read it that is based upon publisher's pre-release material, like a press release kit. In a "preview" you may say what you expect to find good or bad in a book once you have read it but you may not say what you "like or dislike" for the simple reason that you have not read it yet.
A "review," on the other hand, is something you write after you have read a book in which you are expected to say what you like or dislike. The purpose, in theory (not in school work) is to tell other potential readers about whether they should spend their time and money on buying and reading the book themselves ... or not. Your question originally said "preview," but since that presents a logical difficulty since you also mention "enjoy" and "didn't enjoy," I'm supposing you actually mean "review."
A review of a piece of literature has four simple parts. You tell what it is. You tell what it is about. You tell what is technically well done or poorly done. You tell whether you liked/enjoyed it or not and precisely why or why not. Your comments about enjoyed or not incorporate your recommendation, which suggests or outright states whether some else should read it also.
First: Tell what it is. You will include the title and author; the genre; the place in other similar works; and the appropriate readership range or age group. You briefly mention who the main characters are and what trouble [or problem] they face. A simple example of this last is: The three main characters are the Three Little Kittens and the trouble they are facing is that they have lost their mittens and face unhappiness about Mother's pies.
Second: Tell what it is about. Here, you give a simple summary of events. We already know the central characters, so you can plunge right in and simply tell the overview of who does what to whom where when why and how and for what reason. If you don't want to write a tell-all, "spoiler" review [this depends upon your teacher's instructions], you might withhold some of the "why and how and for what reason." Probably though, you will be required to discuss the climax, falling action and resolution, at least briefly.
Third: Tell what is technically well done or poorly done. Examples of this answer these questions. Did the plot make sense to you without confusion in details? Did the foreshadowing lead to an important point or completely give it away? Were the characters presented in a way that you believed in them, or did they seem like paper-doll cut-outs? Did you care about the climax when you got to it? Did the resolution mean something to you? These questions all reflect important technical parts of the structure and techniques of the story, of how the writer organized and developed the various elements and devices. If structure and techniques are well done, you become engrossed in the world of the story. If they are not well done, you generally become annoyed.
Fourth: Tell why you like/enjoyed it or did not like/enjoy it. If you haven't already mentioned it, tell precisely why you did or did not. Examples of this might be:
- I liked it because when the end came, I wanted to read more.
- When the climax came, I felt like I would not know what to do either.
- I felt like the foreshadowing was so bold that I knew what was going to happen from page 10 onward.
Your statements about your opinion either suggest or may directly state whether or not you'd recommend the book to another.