I think that there are 4 categories or areas which must be developed when attempting to master a language: reading, writing, speaking, and listening. I know there are other terms for listening, like comprehension etc. but for our sakes I shall call it listening.
There are two outflows of language, they are writing and speaking. Outflow of writing uses the medium of pen and paper to write symbols which will convey meaning, and the Japanese language is so very much full of meaning.
Start memorizing the radicals of Kanji, this will help you immensely in your understanding of the language, but it may not help your amount of vocabulary. I would suggest this at first because if you try to attack the kanji too soon you might get discouraged, so I say its ok in order to learn how to speak in Japanese a lot of your words will simply be written in romaji.
In order to improve your Japanese, you must make lists and set goals. Lists of vocabulary words to memorize and then goals related to how many words you will memorize.
I set a goal at first after deciding adamantly that I was going to be able to speak Japanese. At the time I couldn't speak Japanese but really wanted to. And since I was already living in Japan, I was immersed. My determination was so high and my motivation for wanting to speak Japanese was so hi, that I set goals, made vocabulary lists, and began my journey towards fluency in Japanese. After lots of hard work, I feel that I finally did it.
I can say it took me 9 months at least maybe 10 before my ears were open enough to hear the small intracacies of the language. But I'll never say that I have become fluent like a native, although when people talk to me over the phone they can't tell if I'm a native or a gaijin. Even the police when they pulled me over twice for speeding when I was doing 45kph in a 30kph, it wasn't until I took off my helmet that they noticed I wasn't Japaneese. Because they couldn't see my face, that I was an American, and because of my perfect pronunciation, it fooled them. They didn't know that I was a gaijin and I almost scared the silly puddy right out of them once they saw my blonde hair.
It freaked them out, that this blonde headed gaijin could speak as a native. But those are the rewards of all my diligence, determination, and steadfastness to my goals.
My very first goal that I made was to memorize 15 words in 2 day.
I did that at first but I did anywhere from 15 -30 words every 2 days, and I would constantly pester someone to quiz me on my new words. The way I memorized words was I made a list of all the useful words I could think of and the list grew very big and then I would do a review over and over, I repeated the words over and over in both directions into and out of English and Japanese, frontways and backwards.
Every chance I got, I would try to use my new words in sentences as the chance permitted. I woke up at 5 in the morning and studied my bootie off, becase I was so determined to master it and be the best I could be as a speaker of Japanese. Next I had two grammar books and learned how to put verbs into bases, then I could just plug and play with my Japanese grammar and my vocabulary list.
I think it also would be helpful to be able to simlutaneously learn and memorize the kanji of a word on your vocabulary list as well as knowing the word just from the romaji. Most often times I didn't have the luxury or time to study the Kanji, so I didn't start a Kanji study until about a year after exposing myself to the Japanese language. I was more concerned with my desire to speak Japanese quickly.
But let me tell you. If you study the radicals of the kanji and just start learning your first year kanji then you will be able to see how words are made and how they may have originated. I mean kanji is a fascinating pictographical way of communicating. To me there is always more meaning in the Kanji of some word as opposed to the shallow no descript meaning of just the phoenician alphabet equivalent.
Before taking on any kanji though, master the kana, both hiragana and katakana. And practice writing the kana, the basic strokes of the kana are related to how and what forms the Kanji.
My secret for learning Japanese fast
Ok I am going to tell you my secret for getting good really fast. It worked wonders for me because I would sit and study, practice my Japanese in an odd way but it was so fun. This is what I did, it may not be like scholarly or a recommended way to do it but it sure worked wonders for me. I would laugh all over town practicing saying the word fart in every type of grammar I could find that accepted verbs. Because verbs are put into the bases I II III IV and V and verbs put into the various bases have various grammars, I would just put the verb, 'to fart' in any bunpo(grammar) I could get my hands on.
For example -
How does one say, "I like to fart"?
You say - Onara suru koto ga suki desu.
I even put it in polite form which to me is really funny. Or you could ask someone,
onara shite kudasai.
"I must fart now!"
Ima Onara shinakereba narimasen.
Or you could have fun saying, "I just farted", Onara shita bakari desu. etc. I think you get my drift on how using the word "to fart" in sentences is funny and useful.
Set your goals to be challenging yet not to the point of overload, neither are productive. If you need a list of words to start memorizing check the link below I have made a word list just for people like you. In essence the more vocabulary you know the more fluent you are (well thats the idea or that is what someone told me once that if you have at least a 4000 word vocabulary you can be considered fluent, but I don't consider anybody fluent unless their pronunciation is perfect). Your storehouse of vocabulary must increase a little everyday. Its important to have someone to check you on your vocabulary too.