I completely agree with the effective ways suggested in the previous answer. Those are a must for a good score. Some more tips:-

1) Structure your answer well. Take some time to structure what are you going to speak. Even if you speak impeccable English, talking in a haphazard manner will give a negative impression. 

2) Use examples, News, Facts, etc you know to answer. I think they do fetch some extra points. Not much brush up little on basic stuff. Try to exemplify using things you know.  

3) Speak clearly but do not try to fake accent. Do not speak as you have just come after binge-watching Netflix for hours :P

4) Practice some sample questions. If possible make a list of some good lines, words, phrases, etc and if possible judicially use them for different possible questions.

Try reading English texts written by native speakers. It will be a challenge at first, but it will be more interesting once you can do it. Practice every day and don't be afraid to listen to something several times to reach a new or unusual vocabulary in there. It's effortless to find free English podcasts online, videos and many more. 

If you can't find English magazines or books, use the Internet to read the news in English every day. Give yourself a reason for studying. Don't be shy in front of the examiner. Enjoy the chat with them. Speak your ideas with confidence and showcase your language skills. Simple ideas which are explained using excellent English can get you to score band 9. 

Remember your past experience and interpret accordingly. Always speak from your heart. Your English is better when you do that. Learn to express yourself using your own language. Sharing your experiences related to topics can be impressive. It is pretty obvious that learning a language takes a lot of effort, but it will be easy if you start liking what you do.

But remember the first thing you need to do is to learn to think in English too. Without it, you’ll always be translating from your native language to English and will take longer to get good at speaking in English.