The best place to start learning Japanese is in a classroom, with a skilled, native-speaking Japanese teacher. This is important because the teacher can introduce the characters you will need to learn and teach you how to pronounce them properly. Japanese has sounds that English doesn't, so it is best to learn them properly from the beginning. The teacher will also have a set curriculum, starting with important basics that will help you build a good base, which you can build upon independently. Starting a language can be confusing, so the teacher is there to clarify and correct your mistakes before they become a bad habit. The classroom also allows students to use what they learn in activities and to be tested on the materials. For local classes try contacting the Japan-America Society; there are branches in many states.
If you have the use of the Internet, you have a very powerful resource at your fingertips. Many sites offer free interactive and printable lessons as well as tips for remembering vocabulary and short-cuts to learning grammar. Since you will have to learn to write in Japanese, you can also print out free writing practice sheets.Text books like Schaum's Japanese Grammar, and CDs like Pimsleur's Quick and Simple Japanese, are other ways to study independently. Because Japanese is such a popular language to learn, it is easy to find good materials in book stores and from online sites. For online classes, with native-speaking Japanese teachers, try the Japanese Online Institute. They also offer online, private classes.
Movies are a great way to not only see into Japanese culture, but to hear how words are pronounced with the proper accent and tones. Movies also let you see the most commonly used words and expressions, not the text book stuff. Books and magazines are helpful because they allow you to see the structure of the language, which will help with writing and speaking. Once you get to an intermediate level, try watching your favorite shows with Japanese subtitles; they are pretty easy to find online.
When you feel that you have a pretty good grasp of the basics, start using it. Try to meet locals in your community; visit Japanese community centers, volunteer at a Japanese senior's residence or go to a Sushi restaurant. Force yourself to speak in Japanese, even if it is broken and basic. Japanese people will be very helpful when they see you are trying to learn their language. Visiting Japanese chat rooms and exchanging emails with a native speaker are also good ways to practice and see how the language is used by natives. Be sure to ask those that you speak with to correct your mistakes.
If you have the time and are an adventurous person, try getting a job teaching in Japan. Japan is expensive, but teaching English there pays well enough for you to live, go out and save a little too. There is no better way to learn Japanese than by living there for a while; it will really bring the language to life. Many people in Japan do not speak English, which will force you to learn Japanese and use it daily. In no time, if you apply yourself, you will be speaking it well and enjoying a new experience.