Yes, imitating is great for acquiring a native pronunciation. Another way would be to study the phonology of the language, in the case of English, starting with individual phonemes, allophone, and continuing with stress, rhythm, intonation, contrasting stress, etc. You can find relevant articles on the Wikipedia (search for "English phonology" etc), and Cambridge has a book, "Clear Speech," that you can find easily in the USA. It would also be helpful if you knew a comparative linguist specializing in the differences between English and Mandarin, or a really good English teacher with expertise in phonology.