How can I properly use intonation as native English speaker?

Hello. I'm student in Korea.
I'm preparing IBT TOFEL recently.
And I have problem working with my intonation.
My pronunciation is not that bad, but intonation prevents me from
getting better scores at IBT speaking section.

Can you give me some solution to solve my problem..
I'm thinking of imitating American drama's lines with video, but I'm not sure
since I love US Drama, but I get a lot of comments on my English intonation..

Thanks for reading, and I hope I can get feedbacks to figure out what to do.
Thank you very much.

What sort of comments do you get?

I read this book to help me with tutoring English pronunciation and intonation. I found it really boring as a native speaker, but I think for someone actually trying to learn the lessons it would be very useful and even interesting. http://aphrohead.com/MediumCover/13587710