By doing things that you find fun. I specially talk about receiving input from shows, movies or books that you like. Songs are also an option.
You could watch movies or tv shows with subtitles in your native language so you get what concept in English relates to what concept in your language. Watching them many times I think also helps, because you don't always get a meaning and memorize a concept the first time you are presented with it.
I've also noticed that learning the lyrics of songs helps. It is fun, which is key for learning. When you learn the lyrics to a song, I believe that you get natural native vocabulary and slangs and you also improve your fluency as you have to keep up with the rhythm.
After that, practice, practice, practice. Speaking if you want to be able to hold longer and longer conversations =D.