The muscles used to articulate the sounds of your native language are not the same muscles used to speak English sounds. Some of the sounds used for English do not exist in other languages.
As you practice English pronunciation, be mindful that you are also training your voice muscles to perform in a manner unaccustomed to them.
Just like doing physical exercise or learning to play an instrument, you must build strength and develop coordination and rhythm. Once again, repetition is key to integrating improvements into your natural speech.
