Decide what your goal is. Do you want to be conversational in spoken Japanese? Do you want to be able to read/write well? What's your target level? Situations? Learning business Japanese is very different from learning everyday Japanese.
Get a textbook you like and stick with it. Study at least an hour everyday. Find CDs you can mimic. Use Skype and find people in Japan you can chat with -- there are plenty of people who will love to do a language exchange with you. Skype was a godsend for me in college; when I was in my second year of Japanese, I spent hours every day on Skype finding people in Skype Me mode and just chatting.
Don't be afraid to look stuff up online. If you want to look something up in Japanese, do it, and then see what you can read. Write down what you can't, learn it, and then you have a context to put it in to help you remember better.
The only really solid tip I have is to learn your katakana and hiragana now. Brute-force it with flashcards and learn them in a week or two. Romaji won't get you anywhere; it's hard for people to separate romaji from their native language (if it uses the Roman alphabet).
Best of luck! Scott
That said, I learned passable Italian (again, similar to languages I already knew) through a combination of self-study and visiting the country. My advice would be to start directly with the hard stuff: studying the grammar rules and memorizing tables of word forms. Of course, the language is more than just the rules, but at least for me it worked fairly well to memorize the rules, internalize them, and then be able to use them in conversation. Hopefully, you've already learned a foreign language, so you know what this process entails. Most books tend to be oriented towards classroom study, so you have to look around in order to find that works well for self-study.
Once you've learned enough to know how to use a dictionary, take a news article and translate it word for word. After about an hour, congratulations, you've just read and understood an article in Japanese. Now go back to studying grammar. Maybe using Google translate and looking at the Japanese text and the translation side by side would be just as good, but I worry it would become too easy to understand.
Much later, once you can understand spoken text, watch movies with movies in Japanese with subtitles. Don't kid yourself and think you'll get much out of this if you haven't already built up a base of grammar and vocabulary, but it's useful for learning colloquial expression and for seeing immediately how the Japanese will phrase things differently from the subtitle language.
Oh, and one other thing: learn the International Phonetic Alphabet. A book will try to guide you through the language's sounds by relating them to your native language, but this can be a crutch because sounds never match up quite right. Start following linkes from the Wikipedia page on Japanese phonology. It's a bit intimidating, but you can start with the sounds which are common to languages you already know and then come back to the more complicated ones later.
As others here have observed, at some point, you need to communicate with actual native speakers. Maybe you can find someone in Japan who wants to learn Spanish (or English?) and you can exchange emails. And, of course, if you're serious, you should someday visit Japan, which will give you lots of opportunities to speak Japanese.
If you're willing to move, and emerse yourself, learning a language only takes a couple months. It's extreme, but unlink almost all other ways of teaching a language, it works.
On the other hand,you may pick up some bad habits: depending on your situation, you may realize too late that your better half swears a lot and you are not supposed to talk like that to their parents, or end up using baby talk with your boss.
It's a great way to get funny stories though :)
Ive been studying Japanese for about 5 years now. I help out at the ruby kaigi here in Tokyo as well with translation. I'm by no means perfect and still have a long way to go but conversation is no problem. My reading is good enough to read blogs and to an extent magazines but novels is a different story ( I'm working on that). So that said here are my top tips:
1) Are you in this for the long haul? If you are then master learning and writing the kanji first of all. Dont worry, its not as hard as it seems. Your a hacker so your going to appreciate this book "Remembering the Kanji" by "Heisig". Use that book with a site called "Reviewing the Kanji". The author truly is a hacker, his methodology of learning the kanji is absolutely brilliant. I finished the book in 2 months and could write about 70% of those kanji from memory. By 6 months it was closer to 95%. I put this off and i regret this so much. I wasted two precious years of studying by holding this back. You learn so much more through reading. Listening too, but with reading you can control the pace.
2) Pour your heart into the above and then tackle hirigana and katakana. If you've come this far learning those will be a piece of cake.
3) Download anki - a vocab software that uses spaced repetitions ( based on the leitner system ).
4) Buy a good Japanese to english dictionary. The Green Godess is good one. A little over the top for a beginner as its aimed at translators but its full of example sentences. You wont need another dictionary for a long time, maybe ever (one day though you might want to look into a monolingual one for children)
5) Grab the Japanese Grammar reference books published by the Tokyo Times. there a set of 3. For now the first one will do. If you want to save money. Tim Kae's online reference is very good.
6) Start learning basic vocabulary and grammar from the above and using Anki to learn it.
7) You could do this by just diving into reading blogs online. Remember you can write a lot of kanji by now so those funny symbols wont be so alien. Use a firefox / chrome / iphone and ipad plug-in called Rikaichan. This allows you to hover your cursor over a word in Japanese and the meaning will pop-up. This is really good. Place any unknown words you really want to learn into anki along with its sentence. Use your dictionary and grammar reference to write notes on the meaning. Anki will then test you on this at various points in time, increasing the interval period to stretch your memory more and more.
8) When you review in Anki, dont just mentally check your comprehension, write out the words to improve your kanji writing and reading abilities. You'll be amazed at how common some kanji are. Its like the 80/20 rule except more like 60/40. Knowing 40% kanji pronunciations goes a long way.
9) Have fun doing this. Find new words and grammar through the things you love. I do it through reading ruby books, techcrunch.jp, engadget.jp and a host of other famous Japanese websites. If you want to find interesting stuff go Japan's version of delicious called hatena.
10) Don't let not being in the country hold you back. There are ways to create your own environment if you try. My Japanese friend found Western roommates and his English has skyrocketed. Try the same in your neck of the woods. Rent lots of Japanese classics, cook from Japanese cooking boks ( cookpad.com ), learn japanese folk songs to sing at karaoke ( search for lyrics online ), build a gundam model using the Japanese instructions, read Ryan Bates Railscasts transcripts in Japanese over at asciicasts ...you get the idea.
11) Search for the language learning forum - I cant remember the name but its big and full of great advice.
12) Above all make it fun!
good luck!
Whatever you do, do not under any circumstances try to learn using romaji. Not sure why but it will cripple your pronunciation. It is easy to tell who started out using romaji... and it is very hard to keep from laughing at their accent.
Don't bother memorizing grammatical rules. Languages don't really have rules, they have conventions. So you can use a grammar reference to figure out what a sentence means, but it will only take you through the basics as a lot of things that people say and write will not conform to any rule.
Make sure you are learning using things you're interested in - comic books, novels, TV shows, music, whatever. Don't waste your time with textbooks (except for textbooks on some topic you're interested in that happen to be in Japanese). When it becomes a chore, you will find excuses to study "later". "Later" eventually becomes "never". To be honest, my knowledge of words commonly used in Japanese pornography is embarassingly good because of this approach though...
The sooner you can switch to using a purely Japanese dictionary, rather than a Japanese-English dictionary, the better. It's very difficult at first (looking up a word, only to have to look up words in the definition of the first word, and so on) but you will find your comprehension skyrocket when you can ditch the J-E dictionary.
When I was 9 and we moved to France I had almost 0 understanding of French. I went to a "school for foreigner" and in two months switched to a classic French primary school. Literally, I learned enough French to fluently communicate with my classmates in two months.
In contrast I was trying to learn German for four years by taking lessons. Without much success. After those 4 years I was able to speak enough of it, but I didn't feel comfortable with the language. What's worse, I was not forced to speak German with anyone (as I was with French). Two years later I barely remember anything.
You need to be forced to do it. Practicing alone will not help much; you need to use the language in order to know it. If you really want to learn Japanese, which I think is quite hard, move there for a few months and get involved with the community. Maybe get a job, join as many groups as you possibly can. Speak, write in Japan (maybe start a blog in Japanese once you know the basics). And go there alone, this way you are not tempted to speak English or Spanish.
These consist of completely aural courses with 30-45 hours of tapes in each language. There are no written materials whatsoever and this is intentional. Dr. Pimsleur's reasoning was that you should learn to pronounce and understand a language before learning to read it, lest you pick up bad habits which will be difficult to lose further down the line.
The courses were designed to teach the most frequently used words in any given language (such as numbers, movement verbs etc.) through sample conversations and drills. Spaced repetition is used to enhance memory.
From the wikipedia entry:
"The student listens to a recording on which native speakers speak phrases in both the foreign language and the language used for teaching (usually English). At varying intervals, the student is prompted to repeat a phrase after the speaker finishes it. The student is then introduced to a new phrase and the meaning is explained. After repeating several times, the student is asked to repeat a previous phrase, along with integrating vocabulary from the new one. More new phrases are introduced, while old phrases are prompted at random, so as to aid long term memory."
I highly recommend the courses, although the downside is that they ain't free.