1. Read, read, and read.
The easiest way to do this is to read about things you like in English. If, for example, you like gardening, then read about gardening in English. You can find all kinds of websites, magazines and books on that topic.
Another way is to read what are called Graded Readers. These are often simplified versions of famous novels. Oxford Bookworms have books in five levels 1~5. Penguin, too, has a similar series. There are also graded readers for children. The Step Into Reading series is recommended.