If you've got the basics down, the best way to go from there is to use and be exposed to the language as much as you can, do things like:  Have regular conversations with a Japanese partner who will correct your mistakes,  listen to Japanese t.v. shows/audio,  try to think to yourself in Japanese and look up or ask about specific things you don't know how to say, begin reading practice and read blogs, news, etc.   (for practice try this:   http://kids.yahoo.co.jp/  )