Practicing to communicate with native speakers in my opinion is the best way to do it.

Yes, Some people can learn by just simply watching videos online but the hard part is when you want to verify and test what you learned. 

I think is not necessary.

I am learning myself by Effortless English menthods and I practice to get accent by the book of ms Anna Cook. This book named "American Accent Training" I think that's an interesting book :x

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In my country, I know one men who that I am very expect. He learned E by himself and he is very famous in Youtube. His name is Hung, and his American name is Bill :D He dead about 2 year :( When he alives, he bought poscard in BenThanh Market, and he learned English by watching movie for 3 years :D That's amazing :D

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If u really wanna learn English, if you really love English, you will learn English by your heart, and u can get success. I believe in that :D

Just like you learned your mother toungue outside of the classroom and from listening to your parents and siblings, you can learn another language the same way at home, with the way the internet is now with the world and information literally at your finger tips this is very possible.  

If we attend a language class, we can share learning with other classmates, get motivation from the learning situation and can consult the teacher. If we have strong motivation and can discipline ourselves, we can learn on our own. What we need are a dictionary, a textbook, a phrasebook and audio materials.

Dear Sepide, Participating in italki discussions could really help u, And u can follow me and recieving some hints,                                                                                                      Best wishes