The best way to learn to speak Japanese is to take an intensive Japanese immersion course in Japan. Japanese is a grammatically difficult language, and without the daily exposure of living in Japan, most people never learn to speak it fluently. There is also a significant cultural component of learning to speak Japanese, which can only be fully acquired in the country. Living with a Japanese host family during your immersion course is an excellent choice, not only for the extra exposure to Japanese, but also for that critical cultural component.
Because of the difficulty of the language, you should expect it will take time for you to learn to speak Japanese. The structure of the language is different, and there is very little shared vocabulary with any other language. That means you’ll spend hours wrapping your head around new grammatical structures and memorizing vocabulary. It also means you’ll need lots of exposure to spoken Japanese, and lots of opportunities to speak Japanese in order to cement things in your mind. If you’re determined to learn to speak Japanese fluently, a one year Japanese immersion course would not be excessive.
If that kind of investment is out of your reach, you can still work on your spoken Japanese by finding a language exchange partner online or a language club in your area. You can improve your listening skills using video clips and movies, and even practice memorizing some of what your favorite characters say to get a feeling for the rhythm of the language. But if learning to speak Japanese is your priority, there’s unfortunately no replacement for going to Japan.