I feel pretty comfortable giving general language study advice, since I've done so much of it, but my knowledge of Japanese study is only second hand, watching my son. I do know that writing and reading are one of the big challenges of the language, as I see how much self-study time he has put into that aspect.

Also, I think previous language study is a big help, mainly because you gain the confidence, and your brain knows how to learn already. My son, for example, already spoke Spanish, and just started studying abroad in a Spanish speaking country a couple of months ago. That process has helped a lot with Japanese.