1.Watch English movies,become jealous of the movie stars,they are also human,if they can speak English so well why cant you?
2.Learning a language is not only learning about its grammar/composition but also learning about the culture and society.read books/watch Tv shows
3.have a good reference point for good English.for example,watch BBC world,Read Books by good authors etc.
4.as somebody already has pointed out,think in english,we bengalees especially have a very bad habit of thinking something in Bengali and then translating in English.don't do that
5.yes people generally have a very bad attitude towards English speaking.They think the person is snob.when something happens like this to you,just think that idiots always avoid knowledge.they are the losers not you.
6.trust me english speaking has a lot of advantages too.try speking fluent english in any place where english is not spoken at all,you will get instant attention