Studying from textbooks can be effective, but it can also get tedious and boring. For many people, finding some cool Japanese songs can make learning both fun and subconscious.
Have you ever had a song get stuck in your head and you can’t stop singing it? Imagine if the song stuck in your head was in Japanese, and each time you sang it you were internalizing grammar, vocabulary, and pronunciation. Eventually you stop thinking about each individual word and just go with the flow, which is exactly the way native speakers talk.
Many Japanese pop CDs, as well as anime soundtracks, include the lyrics in the CD booklet so you can follow along and get additional practice reading, too.
Another thing you may experience while listening to Japanese music is memorizing some phrases or sentence components even without understanding what they mean at the time. Later on in your studies, you will learn something and think “hey, I know that! It’s in such-and-such song!” And you’ll have instantly internalized it and won’t have to study it because your brain already knows that term, and now you know what it means and how to use it contextually because you’re familiar with it in the song.