In my opinion it is necessity and immersion that drive language learning best.

If you don't actually need it it's hard to be disciplined enough to put the work in when there so many other calls on your time.

For me immersion is the only thing that really works. I can plug away at the grammar and vocab ad aeternam without making a den in the task but having to use the language to order a beer or food or talk to people who don't speak your language to get things done works much faster.