Create a timetable. Assign at least an hour a day to learn Japanese and get into a routine sticking to the plan. Japanese has a different alphabet and different letters from English, so you will be starting from scratch. To learn fast, you will need to put plenty of hours in to learn quickly.
Perform research online and find out what resources are available. Pick a few websites that meet your requirements. For example, japanese-online.com, freejapaneselessons.com and easyjapanese.org offer free lessons.
Use these websites and work through different lessons. Pick one to work through its entire set of lesson plans, but also refer to the other websites regularly to support your learning.
Use multiple forms of learning to progress quickly. For example, easyjapanese.org has flash cards and quizzes combined with grammar lessons. Whereas, Japanese-online.com has audio files for you to listen to and then practice pronunciation. At freejapaneselesson.com you can find a Japanese friend to converse with.
Refer to an online Japanese dictionary regularly for words or phrases that you do not know. Do not overlook them. Instead look the word up online so that next time you know what it means.
Track your progress by doing online Japanese tests. Monitoring how much you are learning will give you confidence and demonstrate how much your hard work is paying off.