I recently have tried to learn Japanese, and can pass on a few tips.
The first thing I would recommend trying to learn is the written language. Of this there are three forms: Hiragana ('Traditional Japanese'), Katakana (For borrowed and modern words), and Kanji (The advanced characters). I worked on this by just trying to learn five characters a day, and then constantly repeating them until the whole set was memorized. A good reference, at least for the hiragana, is http://www.thejapanesepage.com/, which has decent exercises to remember everything.
After learning at least the hiragana and katakana, you can start working on grammar and vocabulary. Two books I used for grammar were 'Japanese Step by Step' by Gene Nishi and 'Easy Japanese' by Jack Seward, both of which I recommend. I also used the Rosetta Stone software for a little bit, although found it a bit difficult. All it does is show you a picture and has you say a phrase associated to what's going on in the picture with little explanation as to what is being said.
The one thing I truly wish I had was a tutor to check myself against instead of flying blind. At times, I feel like if I were to go to Japan and try out what I've learned, I'd end up like that guy in the Monty Python skit saying the dirty phrases instead of the true language.
Most importantly, if you're really serious about learning Japanese, stick with it! Make your learning a fun experience!
Steve-
Love makes the world go 'round, with a little help from intrinsic angular momentum.