Preparing for IELTS Test

I'm a college student and I'm preparing for the IELTS examination. IELTS includes listening, speaking, reading and writing. The most difficult part for me is speaking (though other three parts are not my strengths.....) because you don't have as much time to talk to a native English speaker. Besides, as a Chinese person, it has deeply taken root in your mind that the way you think or speak or talk has a strong Chinese style. I wonder how could I finally speak English as good as a native English speaker?

The other problem is that I always prefer to use some advanced vocabularies, although I have no idea whether foreigners use them. How to find a balance point between understandable and gorgeous language?

And a tiny wish at last, can you please tell me the difference between "can " and "could" please ? I'm really confused about it at times. Thank you !

Wish to be your friend and have an audio communication with you!

Please note: gorgeous = beautiful. I have assumed your meaning here but it might not be what you meant.