I remember the first book I ever picked up was Essential Japanese Grammar by Everett Bleiler, but... well, it only teaches grammar (that's not a bad thing, mind you), and everything in it is in romaji (odd, but again, only for grammar). You'd have to go elsewhere for the characters, but you'll get that in your first year. I dunno if it's the best way to go about it, but that's what I did.
Get something that'll give you an overview of basic Japanese grammar and make sure you're familiar with it. Fill in the blanks as you learn your first year, and it should be relatively smooth.
One point advice...
This is not a short road, and it's not an easy one. How long was it before you stopped asking your mom what something meant in English? Yeah, repeat that process. ^^;
Grammar is more important than vocabulary starting out, I think. Being able to relate words with a dictionary is better than knowing the words but not how they relate to each other, I think.
Particles are important, but the kicker is some of them are more understood by gut feeling rather than by logic. Just keep absorbing material, you'll gradually learn by example and get a feel for them. This applies to regular words too, by the way. Connotation and denotation and stuff.
Keep your mind open. Even when a word is mostly a 1-to-1 translation from English to Japanese, the Japanese might view the concept slightly differently. Be ready to rewrite how you think.
Whatever you might feel about kanji, you must learn them to learn the language. Don't worry, they tick a certain way so you can make them work for you. Again, be ready to rewrite how you think.
Sheer memorization will be involved. You'll have to power through this.
Observe. You might see patterns.
... Of course, having said all that, I'm still doing like, all of that.