Alright, here's some tips:
1) Enroll in a class as soon as you can. Trust me, regardless of what you learn beforehand, your comprehension will skyrocket once you've gotten lessons from someone who knows the language (especially if it is said person's native language).
2) Learn the Kana (Hiragana & Katakana) first, before you learn ANYTHING else. Trust me on this, you want to get rid of romanji right away. Only use romanji when studying the Kana. After that, it's best to use it as seldom as possible (ideally you'll never use it again, but that's not always the case).
3) Be aware that Kanji is very challenging if you've never had any experience in that kind of thing before. Sure, it won't be so bad when you first start, but after a while, you'll start to see what I mean. I'm not trying to scare you away from learning, it's just something you need to realize before you jump in.
4) I wouldn't waste my money on Rosetta Stone if I were you. To be frank, it's just not good for anything other than some European languages.
5) Learn how Kanji works before you start learning the actual characters. Understand what kunyomi (訓読み) and onyomi (音読み) are, as well as how radicals work. I'd suggest investing money in a Kanji dictionary as well, but for simply looking them up, online dictionaries work wonders (just be sure it has a good radical filter). Flashcards will help once you start learning the characters, but don't rely on them too much, as kanji have multiple pronunciations; and kanji compounds can make trying to break down kanji from the individual flashcards rather pointless.
Here are a few decent sites that you can use to start learning:
The Japanese Page | TheJapanesePage.com (good for kanji and kana)
Nihongo o Narau - Learn Japanese (good for kana and vocabulary lists)
Japanese Grammar Guide | Tae Kim's Guide to Learning Japanese (good for grammar)
Japanese Kanji Dictionary (good dictionary)
Another thing that you might want to note is that most online sites (and textbooks that I've seen, for that matter), use "printed" style. Now, this won't effect you too much, but there are a few differences between that and "handwritten" style. Unfortunately, I'm having difficulty finding a particularly good image to show this with, but I'll get back to you when I do.
EDIT: One last thing I should mention, textbooks such as the Genki series and Nakama series aren't very good choices for self-learning. They should only be used if/when you take college courses in the language. Even then, the textbook that I use for my class (Nakama) is only used as a supplement to the professor's lectures.