Reading is very important if you want to improve your English quickly. It shows you hundreds of examples of good grammar. It also teaches you a lot of vocabulary and expressions. Seeing the same words again and again will help you remember the words you learnt in the past
Reading can also be great fun and a way to find out about culture and history. Of course you can read newspapers, magazines and articles on the Internet but often they can be too difficult. One answer is to read a book that has been specially written for learners of English. These are called graded readers.
Oxford University Press (OUP) and other companies like Cambridge University Press, Heinle, Macmillan, Penguin and Scholastic produce a wide range of graded readers from beginner to advanced level. There are usually 6 levels of reader that you can buy. At beginner level the vocabulary and grammar is very limited. At advanced level, graded readers start to become more similar to the books native readers enjoy. The readers can be novels, factual or based on TV or film.
To practise reading quickly you could try a relatively easy reader but if you want to build your vocabulary, I recommend you try a reader where you have about 4 new words per page. This means you can learn new words and phrases but also enjoy reading.
Here is a link to the OUP readers website where you can find out what level you are by taking their short reading test at different levels Oxford Bookworms level test
When you have reached level 5 or 6, you could start to read normal unsimplified English novels. Choosing books with a lot of dialogue is a good idea because this will help you with your speaking too.