Well, the first thing is usually to record yourself and listen to how you speak. I'll assume you have done this already. :) Then, compare it with how a native speaker says the same dialogue. The other thing is to make sure you are pronouncing the sounds properly. Many learners (of any language) think it's OK to use the sounds they are familiar with in their native language, when it's actually quite different in the second language. I've personally gone through this issue many times, and substituting the sound with what I know simply doesn't work. There are many videos online on the pronunciation of English sounds, so have fun searching!

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