Listen and copy. Record your voice, listen to the difference between your voice and that of a native speaker, then record it again until you are satisfied. The key to good pronunciation is listening and practice.
The other important thing is to not listen with ' an Italian ear'. For example, an Italian learner complained last week that the English words 'us' and 'as' were the same. They're not - they are completely different sounds in English , but he couldn't 'hear' the difference because he was 'filtering' his understanding of English through his idea of Italian phonology. Try to listen to English with an open mind, not a mind that has been conditioned by your own language. And once you can 'hear' English well, you'll be able to pronounce it well too.