Spend a lot of time listening to native speakers of English. Observe the way they use words, phrases and idioms and construct their sentences. Listen to speakers on television chat shows and watch English movies. This will help you understand how people speak natural English. Although listening to news reports on television and radio can help improve your vocabulary, remember that the English there is more formal and hence, will not sound natural when you use it in everyday conversation.
Read blogs and websites with information on topics of your interest. Most sites on the Internet generally use informal English. Reading such content will give you more exposure to how natural English sounds. Interact with people on online forums and social networking sites. This will give you an opportunity to try your English skills in written form, which may be less intimidating than actually speaking.
Join an English learning community, such as the Effortless English Club (see Resources). Practice speaking with other people in the group using the language you learn from your efforts at listening. Speak to friends who are native speakers of English and ask them to correct you when you sound too formal.
Avoid the temptation to translate literally from your native language. Grammar and the order of words in a sentence will often vary considerably and you will end up saying things that make no sense to the listener. Instead, learn a few phrases, sentences and idioms that are commonly used by native English speakers. Websites such as TalkEnglish (see Resources) have a list of such phrases and examples of how to use them. Practice using these by speaking to yourself in front of a mirror or try them on your family and friends.
Don't focus on the grammar and sentence construction. Trying to speak English in accordance with the rules of syntax will make you sound unnatural. Concentrate on using short sentences that convey your meaning without bothering with flowery language. For example, instead of asking someone "Have you completed compiling the material for the history assignment?" ask, "Finished your history assignment?"