What is the best book (work of fiction) for learning everyday words? without high-flown style I mean
I suggest magazines (People rather than Time) or newspapers (USA Today rather than The Washington Post) if any are available. As for literature, George Orwell's Animal Farm is used in many ESL classes.
Tatti4ka What is the best book (work of fiction) for learning everyday words? without high-flown style I mean

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You can read Animal Farm online for free at Project Gutenberg (Canada) and Project Gutenberg (Australia): http://www.gutenberg.ca/ebooks/orwellg-animalfarm/orwellg-animalfarm-00-h.html


It does not seem to be available at Project Gutenberg (US)
http://www.gutenberg.org /, but there are many other works that are.
You will see that you can find an enormous selection of works at these sites. You can browse, and find something that interests you to read. You won't find many recent works, because Project Gutenberg focuses on works that are out of copyright, but nevertheless there are tens of thousands to choose from at these three sites.

Edit: Here are the main site links for the Australian and Canadian sites:
Gutenberg Australia: http://gutenberg.net.au/plusfifty.html

Gutenberg Canada: http://www.gutenberg.ca / (Scroll down past the copyright message to find the catalog.)
 CalifJim's reply was promoted to an answer.
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You can start with Word power made easy by Norman Lewis which is the best book to learn by etymology. Alongwith that keep reading newspaper and try to learn the tough words from there.

I liked a lot “To Kill a Mockingbird “ by Harper Lee. This book is classic, incredibly interesting and quite understandable if you’re not a native English speaker. I had no troubles reading it. However, if you want to know as many everyday English words as possible, I’d recommend you reading newspapers, magazines, and other modern sources of information. In such a way, you’ll be familiar with words and phrases English speakers are using the most. Because of working on a full-time job, quite often I don’t have enough time and efforts to read books, I prefer reading short posts and interesting articles just on the web. Try it. It’s pretty effective!