Lots of practice. The best ESL speakers I've met all have the same secret: sitcoms. Watch sitcoms, repeat the lines until they come out of your mouth as easy as breathing. You will also learn the more important (and difficult) parts of English such as intonation, sarcasm, and slang. These days, people are watching Big Bang Theory, but I would recommend Friends because Big Bang Theory has a lot of science talk. Friends is much more casual. It's very easy to find the show online and get great subtitles.