Learning something new is complex, because you are dealing with not just one thing, but with a set of interrelated skills. For language, those include correct pronunciation of the sounds, sentence order, sentence melody, usage of verbs, expressions, and so on.
Try to improve all at once and you will achieve little. While the post I’m reblogging is about learning Chinese, it can be applied to learning any other language, and way beyond that, e.g. learning to drive a car, or learning to swim.
In fact even beyond just learning. I get a lot more stuff done in a day if I make a list of narrowly defined goals first thing in the morning. So I completely agree with what Olle Linge from Hacking Chinese advises:
I suggest that we should focus on one or two things at a time. For instance, if we have language exchange planned for this afternoon, we could decide (and tell our partner) that tones should be the focus of today’s practice. If you focus exclusively on getting the tones right, it’s likely that you’ll start making other mistakes. This is okay, indeed it’s to be expected and a sign that you’re doing things the right way.
The post also talks about how some teachers / instructors unknowingly can stand in the way of your progress by not abiding to this philosophy. Find the entire text on Hacking Chinese, and have a look at other articles as well. It’s an excellent blog about how to learn languages, not just Chinese.