Go to a free website, download a set of podcasts or find a textbook for learning Japanese (see Resources). Free websites probably can't help you become fluent, but if your goal is simply to learn the basics, these websites can teach you standard vocabulary and introduce you to the way Japanese is written. Podcasts give you a better sense of the pronunciation than simply reading, and you can take these along on your way to work or listen to them while waiting in line. Search for used introductory textbooks in a local or online bookstore.
Spend at least an hour a day working on your Japanese, either listening, reading or writing. Make flash cards with Japanese words and place them around your house to cement vocabulary into your memory and develop stronger associations. When you see an object or hear a simple word, think about what it is in Japanese. Focus on learning words and phrases that will be useful to you, and don't get hung up on grammar unless you plan to continue learning the language.
Practice using your simple Japanese by reading a Japanese children's book, glancing at a Japanese newspaper or holding a basic conversation with someone else who knows Japanese. Look for fellow students if you are in school, or ask your co-workers if you have a job. Using your language in as many different venues as possible will help even your simple Japanese skills stick with you.
Review the vocabulary and phrases that you have learned by incorporating them into new information. For example, if you just learned several new vocabulary words and you want to learn how to begin writing characters, begin by writing the words you just learned.