Studying/using the phonemic chart helps too :) http://cambridgeenglishonline.com/Phonetics_Focus/

"How can I improve {my} pronunciation in English?” - Correction of your question in between brackets. The key to learn or improve pronunciation is to study the mouth motions of speakers that moves in a certain way, and furthermore the hearing thus subsequently mimicking of the sound. If you can understand the International Phonetic Alphabet, your close to practicing it yourself, without much observation, but in my case I've learned it without specialized phonetic alphabets, the problem with those languages is nothing can be that universal, so it's kind of relative from the native or original language people learned beforehand. So, that gives you two directions of learning/improving, cause you see and hear or only hear or only see pronunciation, but the best is undoubtedly the combination of both. I would advice you to pick and choose one of the English language officials: (US, British-UK, Australian, Canadian etc.) and stick with that until you're satisfied of improving, so far that people generally could understand it. US English works the best for me, because I'm most confronted with this type.

just by listening, keep listening to series by English subtitles

The answer is clear for me: As many hours of listening as possible and repeating out loud. I don't think there are any shortcuts. ^_^