I've been studying off and on (mostly off) for the past... nine years or so.
The hardest part of Japanese is learning the kanji, then the kana, and then everything else is fairly simple as the grammatical structure is pretty straightforward, and the number of irregular verbs in Japanese can be counted on one hand.
As far as memorizing kana goes, just writing them over and over and quizzing on flashcards worked well for me.
I'm still working on kanji, so I don't have any tricks for that.
As far as learning the words and the grammar, I took a couple classes, own a couple books, and I watch/listen to a lot of programming and music in the language so I can hear it being used.
I'm saving up to invest in Rosetta Stone, because I hear it's a great way to learn.