4 Answers

Watch a lot of English TV and movies........(British and American).........

Watch the news....the anchors speak very good English and enunciate well.

By reading litereture(english) more and consult relevant materials to excell.

In addition to these very good answers, enroll in an ESL class and talk with the teacher about some private time to improve your speaking.  
I really believe the best way to get better is to speak English, ask others to speak English around you, and engage someone you trust to correct pronunciations and grammar for you.
READING aloud with someone is an excellent way to speak (and read)better.  It may sound silly, but get some of the word and picture books for toddlers.  It helps you understand as well as speak.  Richard Scarey (maybe it's Scarry or Scarrey) has some really nice word/picture books.
A "thesaurus" provides an excellent way to increase your vocabulary through synonyms and antonyms.   
GOOD LUCK!   English is allegedly one of the toughest languages to learn.  I applaud your desire to be proficient.