Just speak to everyone you find around you. Make as many Japanese friends as you can. The best way would be to speak Japanese with them. Ask them to help you correct any mistakes that you make. They can be your best mentors. As they correct your mistakes, you will learn something new. It gets easier after a while. The more you speak, the more fluent you become.
You can also watch Japanese animes or videos with subtitles. They are good because they can teach you speak casual Japanese. They can really help you because you can watch and learn at the same time, which makes it casual and fun.
