Dear Arun, Read 2 to 3 English Newspapers daily. Always carry a dictionary(Oxford Dictionary/Webster's Dictionary). Learn ten new words everyday from the dictionary, look upto the meanings. Practice using those words in everyday conversation with friends/colleagues. Read short stories, solve jumbles, crosswords. Games like scrabble help you learn new words and enhance your vocabulary. You can buy it from a book store or a stationery shop. Dictionaries have stress marks/phonetics)that stress on the word that needs to be emphasized while pronouncing. You will find a '/' line on the letter of the word. This indicates you have to stress the word while spelling it out. You can even buy Roget's Thesaurus and Effective Communication Skills by Dr. Keval Kumar.
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arun read news paper loudly standing in front of the mirror..Record your voice in a mobile phone recorder or tape recorder and then listen yourself...Keep practicing for a month ,half an daily..You will see difference to a great extent