I've been teaching English over the past 8 years in Japan, private and group lessons,
beginner and advanced, experience have told me that to became a real bilingual, you have to start by mimic native speakers, is not important what they say but how the sound. The first step to acquire a real English pronunciation is by imitation.
Notice that I say "Real" and not "accurate" because accurate pronunciation is different from real, "accurate pronunciation" is easier and anyone can easily learn it, because is more phonetic such as Spanish, Italian, Rumanian, French and JAPANESE among others unlike English which is based on consonants, and for that, Japanese Students and their peers in similar phonetic languages make a great effort to acquire those new sounds for them.
So, to learn English with accurate pronunciation you do not even need a native English speaker, but a good English Teacher (and there are many Japanese who are good teaching English, their grammar is excellent and their pronunciation is accurate, though in most of cases they are not fluent), same happens with electronic dictionaries or e-pencils with voice (like the one implemented by the "Kumon") , but again those won't make you fluent either. to be fluent you need to have a "real" pronunciation, not and accurate pronunciation. Let's face it, native speakers, (most of them) do not speak accurately on regular basis conversation, in any language, and that's why students do not always understand what they say out of the classroom. So to be fluent you need a "real" English pronunciation, how do you do that?
1-living overseas for a while. (in two or three years you'll find the real sounds)
2-having a English teacher, native or not but who has lived overseas and UNDERSTAND the differences between "Accurate" and "Real" pronunciation. And who can teach you both (like me!)
3-Watching a lot Hollywood movies, listening a lot of pop American music and using like crazy the Internet sites where English is Spoken.
And the last and most difficult option is..
4-to find a boyfriend or girlfriend who do not speak in Japanese with you.
I hope this writing can be of some help for you, keep on trying and enjoy English, remember Learning English most be Fun and Interactive!