Well since i've been asked so much and since i've seen that my idea has been floating around a lot too I think is time I compile a step by step guide of how to practice Na'vi, the Shiaru way.
Step one:
Make a journal and try to write at least a sentence on Na'vi a day on it. (this is the idea that everyone is talking about, I really like the fact that everyone is using my idea. It really helps).
Step two: Try and use a new word, repeat said word at least 10 per hour. (you'll find yourself being able to identify it on the spot later on, and using it unconsciously).
Step three: Listen to a particular Na'vi excerpt from the movie with subtitles then try and repeat the intonation and the words as best as possible. (this could take many tries so use s mall sentence if possible.) Then write it down while listening to the excerpt.
There are more steps that I will write down later, If you go an idea reply with it, comments appreciated as well.

Remember this method works thanks to Immersion, a state in which the human brain believes Na'vi to be important and thus will commit resources to learning it unconsciously. If you would like to know more on how it works ask me and i'll be happy to answer.