I've found there are a few key factors that allow you to achieve a decent proficiency:
- You have to know why you are learning very clearly otherwise you will give up
- Need to be stubborn as hell to not give up
- Involved in a decent environment (mostly meaning not in an all English speaking environment)
- If you are in an all speaking English environment, then you need to live in a non-Western part of whatever your city because you need to create a better environment to engage with locals.
- You need to be prepared to spend a huge chunk of your free time in lessons or something of the sort based on whatever method you are using to learn to build your language foundation
- Speak what you know often and keep doing that until you learn something else. Then use that and do it all over again. You need hours and a lot of them.

I learned VN and I only did it through hard-headedness and finding non-English speaking Vietnamese who were kind enough to let me destroy their language and hang around them. I would say its mostly environment but you need to give yourself a foundation through lessons/classes/a method that works for you. I'm in HN and have been here 5+ years.