How can I better learn a new language?

Learning a language by using it is the most efficient way. Having a partner to practice not only help you work on your pronunciation and accent, it also incentivize you to keep practicing (similar to how having a gym buddy makes you go to the gym more often). 

Language are also meant to communicate. Allowing yourself for mistakes, whether it is an accent, bad conjugation would allow you to keep practicing and would result having a broader set of words and sentences you can use. From there correcting mistakes becomes easier as you naturally find relations between conjugation, forms etc.