I had given the IELTs long time back...and I am not a native speaker. I didn't attend the trainings of some schools or institutes, neither did I go for British Council coaching classes.

I improved myself thru pure reading in English, taking some comprehensive examples, going to various descriptive compositions/essays etc. As for interview/speaking session, the secret lies in how bold and confident you are. If you stammer or lose confidence, it becomes harder...good luck, and let me know if I could be of further help. Cheers!