Start by learning to read and write kana. Then you'll have the basic building blocks. Any kanji you can learn to supplement for the moment would also be great, but at least get the kana down pat.
Then start building your vocab in conjunction with the readings and exercises you're encountering. One thing I did that wasn't so helpful was to start making flashcards using words I thought would be useful, but that I didn't really have any contextual reference for. That is to say, I picked things out of a dictionary that I thought would be useful. These are the beginnings of 'Japanglish' or 'Engrish'. Most times it wasn't a natural word to use in Japanese (regardless of its commonality in English) and there was a better synonym available.
So, researching the words you see in your books and hear from your exchange partners, and having context to go with them will increase the versatility and proper usage of the words you're learning. You'll be learning Japanese that the Japanese use, not Japanese translated from English that English-speaking people use, which can have no relation to Japanese sometimes. The added benefit of seeing them a few times within the reading will help make them stick. Learning difficult words at random just because you know and use them in English will result in archaic translations and misunderstandings.
As you build your vocabulary you'll want to start keeping note of all the 'idea' translations contained within the grammar, so when you have a thought and want to express it, you select the proper construction. Straight translations don't work, so try not to relate directly to English grammar. There's just no way to say certain things in Japanese, and you have to abandon the English construct and learn what the Japanese do in those situations. This is learning to think in Japanese, and it helps improve the spoken language greatly.
If you can get your hands on it, I highly recommend this book for starters:
Followed by this once you're reading more strongly:
I also recommend a high level of review. I spend entire study sessions reviewing and not learning anything new, and I've found committing stuff to long-term memory and not forgetting anything really helps layer my Japanese so subsequent lessons make more sense.
Also, keep in mind that learning occurs in leaps and plateaus. You'll feel slow at first, then all the junk in your head will organize itself and stuff will start to 'click'. Then the next onslaught of material will sit there, rattling around in your head hopelessly, then one day it'll click. So don't get frustrated.
Lastly, I'd highly recommend a language exchange partner so you can actually practice your speaking, as it's quite a different mental environment from the go-at-your-own-pace of reading/writing exercises.
As Damicci aptly pointed out, romaji is completely useless, it'd be like a Japanese speaker trying to learn English through katakana. Avoid it at all costs. Mind you, the first grammar book I mention, the orange Barron's, it's in romaji but only in order to be concise and accessible to beginners. Try to migrate away from that and see the kana syllables contained within the romaji.
That's all I can think of for now, good luck!
