From what I've heard from the people from my regiment (and mind you this was awhile ago), is that one of the best ways to learn it is to listen.
There was one guy who joined our regiment while at the time was still learning English. He told me that joining the regiment helped him at least accelerate his understanding of the language.
I don't know if you're willing to join a Dutch speaking reg, but I'd definitely say having a way to practice it 24/7 in a semi real world conversation, will help you a lot.
Also, I don't speak a drop of Dutch so, Succes gewenst? Shamelessly copy pasted from another site.