Determine your strengths and weaknesses. You will devise your course of study and the materials you gather to aid that study based on your current ability.
Purchase a JLPT Level 1 test preparation book that focuses on your weaknesses. .
Subscribe to a Japanese newspaper (the Asahi Shimbun and Daily Yomiuri are popular) and make a habit of reading it daily. You may also want to buy a few novels in Japanese. Some people suggest buying translations of English novels you have already read.
Get three notebooks: one for writing and reading practice, one for grammar and usage notes, and one for vocabulary. Organize your vocabulary notebook to aid your memory, such as by synonyms and antonyms, grouped in themes (business, economics, politics, etc.,) or pictures to provide a visual cue for memorization. Avoid simply writing down words in the order you encounter them.
Purchase three different colors of highlighters: the first for vocabulary, the second for grammar, and the third for usage or supplementary notes.
Read the title and introduction of each chapter in your JLPT Level 1 test preparation book. This will help you estimate your learning progress.
Write your learning goals at the top of the first chapter. Your learning goals should be as specific as possible: what you want to learn in this chapter and why. Having (and meeting) specific goals will help keep you motivated, provide a sense of accomplishment and focus your mind on the learning task. Repeat this step for each chapter before you study.
Establish a study schedule. Allot at least 30 minutes per day for reading and 30 minutes per day for listening and speaking practice.
Note the differences between spoken and written Japanese whenever you read. Most written Japanese is more formal than spoken Japanese, and the vocabulary used in written Japanese will often be quite different from the more commonly used diction.
Establish the meaning of unknown or unfamiliar words from context before consulting the dictionary.
Highlight each new vocabulary word, write it in your notebook, and enter it into your electronic flashcard program.
Read a variety of Japanese sites on the Internet to familiarize yourself with different formats of written Japanese; for example, letters, public notices, rules.
Write, write, write! Make sure you know the proper stroke order for each kanji. An average Japanese elementary school student practices writing each kanji up to ten times per day, sometimes studying twenty kanji per day.
Check your weekly progress by confirming whether or not you are meeting the learning goals you wrote at the beginning of each chapter. If you are not meeting them, determine why, and adjust your study habits accordingly.
Review synonyms and antonyms while you are walking or riding outside. You may be seen talking to yourself, but don't worry -- it's for a good cause.
Read any example sentences, sentences you've written, or vocabulary items aloud to yourself three times before you go to bed and again when you wake up.
Make an audio recording of yourself speaking vocabulary items or sentences in Japanese, followed by a pause, and then the English translation. Listen to this audio recording outside of structured study time, and try to anticipate the translations. Repeat the Japanese as you listen. As the BBC advises on its Language Education website: "Make your learning an active part of your life. ... you're likely to remember 20% of what you read and 30% of what you hear ... and a staggering 90% of what you see, hear, say and do."
Quiz yourself at least three times a week using the flashcards you've made. Mix together old and new material.