Practice makes perfect. I know it is cliche, but it is true.

Leas en voz alta. Uso los libros para los niños... porque las palabras no son difíciles and aporta mucha buen practica. buena suerte.

I always do pronounce like American accent, when I hear every words. I speak out loudly same they do for many times. It is work for me :)

Shadowing. It's a technique involving copying what is being said. I recommend listening to any material such as the news, radio, native speakers, fluent speakers. The aim is not to get the word correct and to comprehend the text, but to follow the speech patterns and imitate. I found this very effective for intonation. Give it a shot in the target and language and your native language

Every person pronounces things differently and has different problems with pronunciation (even in their native language!). You ought to speak with a native English speaker and ask them SPECIFICALLY to tell you what's wrong with your pronunciation and to work with you to improve it. However, you ought to have a strong base in vocabulary and grammar (that is, you ought to be comfortable speaking the language in conversation) before worrying about your accent.