Learn to write the two Japanese alphabets. There are 45 basic letters for each of these alphabets, though you can add small parts to create a new sound. For example, with the addition of a small circle in the upper right corner, the character "ha" becomes "pa." Write each letter a few times, then combine letters to form words.
Practice writing the kanji. There are thousands of kanji that you need to learn to write Japanese fluently. You can learn them with flash cards that show the stroke order, through a textbook or through a website.
Use kanji to stand in for nouns, verbs and adjectives. In most cases, you'll use a kanji for these things in your sentence. If you are just beginning and do not know a particular kanji, you can substitute hiragana and a Japanese person will be able to understand your meaning.
Write foreign loan words as katakana. For example, you would write "esukaretaa" (escalator) in katakana.
Add particles in hiragana. Particles are small Japanese words that connect or modify nouns and adjectives in Japanese, similar to English prepositions. Write these in hiragana. For example, if you were writing "eki ni" ("to the station"), you would write "eki" as a kanji and "ni" in hiragana.
Conjugate verbs with hiragana. Immediately after a kanji that represents a verb, you'll want to conjugate it with the appropriate hiragana. For example, if you were writing in the present tense, you would write "masu" as hiragana.