Reading books can be a great way to pick up new vocabulary, see grammar in action and develop your understanding of a language. The key to success is choosing the right book for you.
For beginners, I would recommend starting with something short and simple. Avoid the classics for now - they often use archaic (very old!) English words and can involve complex themes. Children's books are a great place to start. Roald Dahl has written many superb books (Fantastic Mr Fox is my personal favourite!) and Dr Seuss's books are guaranteed to make you laugh. Dr Seuss writes his books in rhyme and they are all very funny - The Cat in the Hat is probably his most well-known book. Starting with something like this means you are more likely to finish the book and want to read more.
For more advanced learners, you could try The Hobbit by J.R.R. Tolkien. The book isn't too long and if you've seen the film it may be easier to follow. If you like reading about historical events, Anne Holm's I am David is a short story about a boy trying to find his mother during World War 2. Holes by Louis Sachar is also a great read.
If you're not quite ready to read a full book, why not try Roald Dahl's Revolting Rhymes? This book contains lots of short stories, based on fairy tales, all written in rhyme. Or, try a very short book - like one from Roger Hargreaves's Mr Men and Little Miss series. Although they are intended for young children, they are a good way to pick up some more basic vocabulary.
My final piece of advice would be to read something that interests you. Look at the blurb (the short summary of the book, found on the back cover) and see if it looks like something that you would enjoy. Think about the genres that you enjoy in your own language and find an equivalent in English. This way, you're more likely to enjoy reading, rather than see it as a chore.
Do you ever read books in English? Which book would you recommend?