Start with children's books. If you only know the basics of the language, children's books will be easier to understand and will help you build your knowledge of English grammar and syntax.
Move up in reading level slowly. Young adult books generally contain a guide for the reading level. Once you can read children's books easily, move on to third- through fifth-grade level. Then, move into junior high and high school reading.
Read your first adult books. Nonfiction books can be a good way to start because you won't have to worry about complex literary meanings. Generally, the meanings of sentences will be straight forward and easy to understand.
Look up words when you don't recognize them and cannot figure out the meaning from context clues. Have your English dictionary handy while reading books.
Write down words you see often but are having a hard time committing to memory. The simple act of writing the word down makes remembering it easier.
Discuss what you read with an English-speaking friend. Having discussions about the book in English will help you become fluent even faster.