How to become fluent in Japanese without taking a formal class

Buy the book Japanese Grammar (Barron's Grammar Series) Carol and Nobuo Akiyama and memorize its contents.  This book is a very valuable resource and covers most of the basics of Japanese Grammar. Here is a link .

Step 1

While reading through the first book here is a list of resources that you should download.
Tagaini Jisho- This is very useful when first learning the kana and will remain a valuable resource as you learn the kanji.
Anki-  A very good flashcard program.  The flash cards that will be most helpful are
JWPce- This is a Japanese word processor and is also useful as a dictionary.

After learning the basics of Japanese Grammar from Barron you should learn the hiragana and at least familarize yourself with the katakana using Tagaini Jisho.  Also use the Anki flashcards Master Hiragana (with audio) to familiarize yourself with the pronunciations more. 

You should also try to expand your vocabulary using the Anki flahcards Genki I Vocab Master Deck.  This also has audio so you can improve your pronunciation and listening comprehension. 

You should also introduce yourself to some kanji using the Anki flashcards All Kanji for JLPT 4.  Use Tagaini Jisho as a resource for breaking apart the kanji to manageable parts and for practicing stroke order.