Reading a book, is a very ambitious way to learn a language (especially for beginners) as most books are written using a descriptive or complex language that is very different from how we speak to our friends or coworkers. Think about the classic books in your native language, is that how you speak in your daily life?
However when learning a language, I suggest that you try a variety of methods, until you decide whatever is most comfortable for you. There are some language learners who can read and write well, but cannot speak well, and vice versa.
Many students ask teachers, what is the best way to learn a language, but what is a good way for me to study, may not be a good way for you to study. Try many different methods, but remember learning should be fun!
The ideal is to find a book that is a) extremely interesting to you, and b) is at exactly the right level of difficulty so that you can really read it and enjoy it, guessing most new words from context, and encountering examples of grammar that stretch what you've learned.
I can't say I use a single book--I do almost the exact opposite, I try lots of different things. However, I am learning Spanish, and I am currently reading a book in Spanish translation: ¿Qué pasaría si...?: Respuestas serias y científicas a todo tipo de preguntas absurdas, de Randall Munroe.
Why is this a good book for me? It isn't great literature. It isn't one of the book I would want with me if I were stranded on a desert island. But I like science. I like Munroe's sense of humor. It is relatively easy, because it has technical content that is familiar to me, and does not have foreign cultural content that is difficult for me. Finally, I am trying to understand the conditional and the subjunctive, and this book is about nothing but crazy consequences of impossible situations--how high would you have to throw a steak in order for it to be cooked when it landed?--and therefore is full of examples of the conditional and subjunctive.
(I was struggling with a passage in La Sombra del Viento, de Luis Zafon. I couldn't understand some quoted dialog. I asked my teacher "is that a Catalan accent?" She says, "No, that is " (I think it was) " an Asturian accent, because he is from a neighborhood of Barcelona where people speak that way." Not easy!)
Books have helped me a lot to learn other languages. I always tell my students that the best way to learn is by doing the things that they love doing in their own language, but now in the new language that they are learning. This may mean listening to music, reading blogs, watching YouTube tutorials etc... For me however, it means reading novels and I love the feeling of finishing a novel in a language that isn't my native tongue. I feel a great sense of achievement. Here are some books I recommend for Spanish and English learners:
Juan Salvador Gaviota
Un Relato de un Naufrago
Born a Crime
About a Boy
Starter for Ten