Learn the katakana and hiragana alphabets. These are phonetic alphabets. Typically, the Japanese will use katakana when writing foreign loan words, and hiragana when writing prepositions or other Japanese words that don't have kanji. Early learning material also uses hiragana in place of some of the more difficult kanji.
Use a study guide to begin to learn the kanji. Many study guides construct sentences using only the kanji that you have already learned. As you progress through the book, it will incorporate new kanji.
Learn to use a kanji dictionary. As you begin to read more complicated texts, you won't always be able to "sound it out" when you come across a kanji you don't know. Kanji dictionaries organize the kanji by "radicals," or parts of the entire symbol, ordered based on the number of brush strokes.
Focus on learning the 1,945 kanji that the Japanese government has approved for use in the media. Use flash cards to drill yourself.
Choose a manga books to read in Japanese. These comic books will use kanji, but the images also help you to understand the meaning. It's a good first step for readers.
Add furigana to any Japanese website. By entering a URL into the box at Hiragana.jp, you can add furigana to the kanji. These are small hiragana printed above the kanji to let you know the pronunciation of the kanji. It's helpful for learning kanji that you don't know.
Read other Japanese books that interest you. Order books through Amazon Japan or by going to a local Japanese bookstore. You can find books in all subject matters.