My second language is English (as you can see, it's fluent). I started learning English when I was only 2 or 3 years old, seriously. My mum is a teacher of English so she teached me. I also love English very much and I often watch TV, listen to music and read books in English, that helps. I have many friends from the UK, practice always helps. But the best way to become fluent in any language is to move to the country where this language is spoken.
I just exposed myself to it. I watched news in the language, listened to music, went to bilingual stores.
Practice, practice, practice. ; ' )
Actually, the VERY BEST way to become fluent in any language is to move to the country where they speak that language. You'll be forced to use it every day.
參考: Me. I was stationed in German (twice) for a total of 9 years.
I grew up hearing my grandfather speaking Polish which I am learning to speak through videos, applications, and books. I know Spanish and French fluently and I began to study Russian. I suggest talking to people through conversationexchange.com
I took Portuguese as my minor at university, then took a job involving much reading of Portuguese. Twelve years after that I took a job at a Brazilian university teaching library science (in Portuguese). Doing that for three years proved enough to achieve fluency, but a went on to do a PhD in Brazilian studies which included cold calling Brazilian businessfolk and officials to interview them.
Moved to a neighborhood where no one spoke English. Lived there six months then married the girl of my dreams. Waited another ten months before taking my bride to meet my parents.
I was born next to the Germany, all older people in family spoke German. So early on they spoke German to everyone. Was easy to learn. Italian was spoken in my home city, easy to learn as well.
The I moved to the US and learned English and now learning Spanish since it is so close to French my home language.
I spoked only it all of the day, and engulfed myself in people who as well did so, thus I was able to become absolute fluent-like on English....