Silent

You could do reviews! There’s no magic to it — it’s just giving your opinions. You talk about whether you liked the book, whether it was easy or hard to read, if something about the book bothered you (unlikable characters, too much explanation, confusing plot, etc.), things the author did well (creating a new/believable world, for instance, or really vivid characters), whether you would read the book again, things like that. The only thing I suggest is to try to avoid giving spoilers — or if a spoiler is really key to why you did or didn’t like the book, at least warn people first. Otherwise, I don’t think there are really any rules to it. Just give your opinion and try to be helpful.