hi.there, I m a mandarin teacher. I m glad help you to answer your questions, so if you have any question.you can ask me.
I have some experience I want to share.some students ask me,
how can I get the better accent?
my answer is you need to learn pinyin 拼音，and tune, there have youtube links,
https://www.youtube.com/watch?v=5HjfI0n7JIM
https://www.youtube.com/watch?v=TZe_E796uQw&index=1&list=PLbW7TGqk0vrrKqhzt7F2jIwk6Z6ahoPSR
https://www.youtube.com/watch?v=DLbIXvk7giQ
in youtube have many this kind videos.you can find one fit you.after you watch the video. you will know the where is your problem,but most important thing is you need practice.practice is very important to hlep you have good accent. you can read some words or sentence.you can also find some tongue twist.
