[hikarudo]

Not related to habit formation, but may I say what worked for me when learning Japanese in Japan?

Take the Nihongo Nouryoku Shiken. Bookstores sell material to study for it. It's great having a study milestone.

Start reading, if you haven't already. Books, magazines, anything. A kanji you see "out in the field' for three times becomes yours.

To improve listening skills, I recommend watching lots of jdrama. If you don't understand a dialog, listen again.

And most importantly, interact as much as you can with Japanese people. This is harder than it sounds, because... Japan.