I'm in the midst of learning it right now, actually. Started back in February. I can hold very simple conversations now, but I'm still a long ways off from true fluency. In terms of characters, I know ~250 kanji, which is roughly a tenth of the common usage characters.
My advice: -Your very first purchase should be a kana guide and your first exercise should be to memorize all of them, including the proper stroke order. Hiragana first, then katakana next (92 characters total). These are the building blocks of the entire Japanese language (akin to the Western alphabet) and you use them constantly (Hiragana especially).
-Figure out whether you want to speak Japanese, read Japanese, write Japanese, or all of the above, because they all require slightly different skillsets. You can be great at written Japanese and hopeless at conducting an actual conversation and vice versa.
-Flash cards are a godsend for learning Kanji. Don't bother wasting money on buying a pre-made set; learn the characters and make your own. Way cheaper and it helps with memorization.
-Use some form of audial learning as well (I use Rosetta Stone and a couple of other programs) - some parts of Japanese pronunciation are very difficult to describe without hearing them (lengthening vowels, the tendencies for "u" sounds to be minimized, etc.)
-Try and find someone who knows Japanese. Even if they won't teach/tutor you, you can still use them to figure out if you're saying something you shouldn't be (appropriate level of formality, correct gendering, etc.)
-On that note, Japanese is a highly gendered language. There are some things that men say that women never do and vice versa (for instance, men use the phrase "boku" to refer to themselves in Japanese, while women use "atashi"; both can use the slightly more formal "watashi"). Be aware of that, because it can get you into trouble - I used to attend a cooking class with some Japanese women, who would teach me bits and phrases. Occasionally I'd repeat one of them to a friend of mine who spoke Japanese, eliciting a chuckle and a comment along the lines of "You've been talking with your girlfriends again, haven't you?" - his code for telling me I was speaking like a woman, at which point I'd have to ask him how to say the phrase like a man would. Random aside - I saw an old samurai movie a month ago (can't remember the name) that very clearly had a female translator, because the gruff, hyper-masculine samurai protagonist was talking (in Japanese) like the most flamboyant gay guy you've ever heard. It was an absolute riot.
-Similarly, formality is very important in Japanese. There's sometimes literally dozens of ways to say the same thing, depending on how formal you want to be. Always err on the side of politeness, but learn the various forms so you don't come off like a complete stiff.
I've started with Hiragana and it's slow going.. Kanji looks scary as hell. Seems to me that they are essentially emoji's, but other than memorization, I can't find a logical way to interpret the characters that I can recognize. Guess this is why Japanese students study in a repetitive manner for years! ---