You learn to speak fluent Japanese only through speaking Japanese!
Actually fluency in speaking comes only through rigorous practice and understanding of the body languages and practical uses of the words in public. This again, can be achieved through mixing with the people and try speaking with them in their language in day to day life. Even someone who is never introduced to or nor having any idea of a foreign language, can guess, with some study, what others are trying to speak, just by watching them and studying their gestures when they speaking among themselves. Gradually, he will be able to pick up the words they are using and finally, he will end up using those words in public. The same process must be adopted to learn to speak fluent Japanese.
Don't worry about right or wrong. Just speak out to everyone you find around you. Make as many Japanese friends as you can and try speaking Japanese with them. Ask them to help you correcting the mistakes after you have finished. They may not be able to resist their laugh over the strange and funny words you speak in the beginning. But things will get on easy after some time. The more you speak, the more you get affluent.
A few more things which could help you learn to speak fluent Japanese. First, mimic the Japanese way of life. You will learn a lot of words handling those objects without your own notice. Second, watch Japanese cartoons or read Japanese comics and try understanding them. Finally, keep a scrap-book. Writing helps memorizing the words and places of their application.
