Here are some useful tips:
1. Learn some basic English vocabulary. Learn how to use the natural expressions : for example, Well, actually, It depends, Take your own time, I will be right back, I will come back to you on this etc
2. Refer to some good books on grammar: For example, Essential and Intermediate English grammar by Raymond Murphy (Cambridge University Publication).
3. Read magazines in English or Articles on various topics available on internet.
4. Practise speaking on variety of topics.
5. Join some good English language class. Your teacher can help you with pronunciation and fluency development.