After almost 50 years of studying several foreign languages with varying degrees of success, I have come to two conclusions. First, that classroom instruction is the worst way to learn. Second, that the most important thing is to stop consciously trying to learn. As an example, many years ago one of my guys, after completing 9 months German language classroom instruction, where he was at best an average student, went to work in a small town in Germany. After 6 months there, he was speaking well enough to pass as a native. He did it by spending his spare time down at the local gasthaus chasing women. I, on the other hand, after a year learning the Vietnamese language and two years in country using the language daily but not in a position to use it socially, could never pass myself off as a native. I guess I could never get the pronunciations right.
Being convinced of the correctness of my two conclusions above, I searched the internet to find out why those conclusions may be right. I found that there is some very recent research into how the brain functions that may explain it. Researchers, by scanning the brain, have found that there is a huge difference between how the conscious brain and the subconscious brain functions. I will use an analogy that experts would probably call overly simplistic or silly, to illustrate my understanding:
IBM recently developed a computer system called 'Watson' designed to understand natural, complex English language and respond to questions in real time (within 3 seconds). The system is made up of a large room full of 90 servers capable of parallel processing (carrying on many tasks simultaneously) and accessing many terabytes of data. Think of this system as the 'subconscious brain'. Then consider hooking your laptop computer up to the Watson system. Think of your laptop as the 'conscious brain'. Obviously, if you needed to input large amounts of data into your brain, you would want to directly access the main system, the 'subconscious brain'. Inputting the huge amounts of data making up human language through your laptop, the 'conscious brain', would take forever. There are estimates that the 'conscious brain' only has about 2% of the capacity of the 'subconscious brain'.
Another example of the difference between conscious and subconscious (or non-conscious) activity would be the simple act of picking up a beer. The conscious brain makes the decision to pick the beer up. The subconscious brain directs the movement of the muscles to actually pick it up.
Young children learn much of what they do (as quickly as they do) because they apparently have direct access to the subconscious brain. Thus, young children can rapidly learn any language. As we get older, consciousness gets in the way of the subconscious brain, making learning (especially languages) much slower and harder. Experts believe that distracting consciousness increases subconscious brain activity and that the brain is capable of flipping quickly and frequently between conscious and subconscious.
So, my way of learning is not so much to memorize vocabulary or conjugations, but rather to place myself in situations (preferably social) where I simply must speak the language. Distract the conscious brain so that the subconscious brain can do its job. I found that a beer helps.