Most Japanese youngsters speak the kind of Japanese that is not taught in language school. The “masu” form of a verb is used only while speaking to superiors at work or probably while speaking to teachers at school. 80% of the time it is the plain form that is used while speaking to colleagues. Even if you spoke using “masu” form, your colleagues might still reply using slang and informal Japanese. Watching dramas is a good way to pick up spoken/ informal Japanese. Did you know that the site www.dramanote.com gives the complete dialogues of old Japanese dramas? So, when you hear a dialogue that you don’t understand, you can read the same in Japanese and look up the meaning “word by word” in a dictionary. Works similar to watching a movie/drama with Japanese subtitles. The site also gives a brief narration followed by a brief observation on the drama/movie. Definitely helps to pick up reading comprehension skills too.