Hi, Pooja,
You can improve slowly but surely. I suggest you read the newspapers like The Hindu, Times of India, etc., any of the leading dailies in India. Once you can speak good English, then automatically your problem in writing will be half solved. To be a good writer, you really have to have a command over the basics of English. First of all, try to become strong in basics. Once you are confident about your knowledge, you can speak English fluently. There is no point in stopping yourself if you feel confident about the basics. Reading newspapers and listening to news channels like CNN, NDTV, etc., will also help your cause. Try to speak in English, even though you might make mistakes. Mistakes are bound to happen. Nobody is the best in English. It's an ocean. It's a learning process for all. There are a lot more things to learn in English that are left, even though you feel you are the ultimate in it.
All the best, mate. Hanuma