"How can I improve my English pronuncation?"
To be honest, I think you should get feedback from a native speaker who can actually help you. This means someone who can tell you what your errors are, and how to fix them.
Aside from that, do record yourself. You may not like what you hear, but it's what everyone else hears (and we're probably not horrified, so don't worry too much). ;)
you can use websites like : www.engvid.com
when i learned and studied English, one of the things i liked to do on my own was to just read texts out loud and slowly enough to actually focus on rhythm, stresses (accents) and pronunciation.
then i moved on to college and English became my major, so i had classes in a lab with a teacher, but one of the things we were asked to do to prepare our sessions in the lab was to look up the phonetical pronunciation in a dictionary (each entry usually has a phonetical transcription) of each word. reading the alphabetical alphabet is not that hard (i can help if you want) and if you invest the time, it really, really pays off. then, it's a matter of just playing the game and diving: "i'm an English-speaker"...
i am French and people still tell me i have no French accent when i speak English, i am sometimes mistaken for a native speaker. not to boast but to tell you how focusing on pronunciation can yield results. it's like developping a good ear for the right sounds and reproducing them, like a musician.
I think you need to focus on two strategies:
1 - Listen, listen and listen. Download every podcast that you can. I recommend the following: ESLPod and All Ears English (American accent) and BBC 6 Minute English (British Accent).
2 - Find a tutor on iTalki. Specifically any teacher that is focus on pronunciation. I recommend this guy: http://www.italki.com/teacher/1576629
practise is the only way to improve your conversational skills, also you could listen to the native speakers accent and try to imitate it, also it is useful to record you speaking foreign language and compare to the native speakers accent, pay attention to the differencies between yours variant and one produced by native speaker and practice more.