"Ain't" ain't a word. My high school English teachers pounded that into my head. And they were right — "ain't" is not proper English. On the other hand, it is used colloquially by people all over the English-speaking world. Language is not just limited to those words found in reference books and textbooks. Whether formally recognized or not, utterances people use every day are language. So if you're working to improve your overall Japanese level, you might consider learning just a bit of what, strictly speaking, ain't proper Japanese.
The Japanese language is brilliant at accommodating abbreviation. You can almost always make words or phrases shorter. And it will undoubtedly raise your perceived, if not actual, fluency. Doing so will also help you break free of grammatical constructs that at times make you sound like a fuddy-duddy.
Here are some examples I've collected through my experiences as a homestay participant, then as a student of the Japanese language, and now as I live and work here in Japan. You probably hear some of these constructions multiple times a day if you live in Japan. (If you don't recognize them, you will start to once you're aware of them.)