I’ve taken Japanese for 2 semesters so far at university. I was never a huge anime or manga fan; I guess food was the biggest draw (see username.) Also, I’ve lived in London and quite frequently travel to Europe, so, being a lot more familiar with European culture, history, and society, it was something a little different. Plus, it would be cool to live there for a year or two, I think.
I made flashcards for kana and it took a few weeks to learn, but a few months to get down to instant recognition. I would recommend doing katakana now also, because the faster you start the sooner you won’t have to worry about it. A good site for kana, and for kanji when you get to it, is http://www.kanjisite.com/html/start/
The grammar can be quite confusing at first, because the sentence structure is so different from English, but as you get used to it, things start to make sense. One big challenge is kanji. At first I was resigned to never really knowing them. I would just memorize “this one has something that looks like a ‘b’ on the left and lots of vertical lines on the right” and get through a quiz. I realized it would be stupid to be spend so much time but be pretty much illiterate, so I started putting a lot of time into it. One thing that helps is learning the radicals. A book that uses “stories” to connect the radicals in a character to its meaning is Remembering the Kanji. The first 200 or so pages in a pdf is here. I personally didn’t use this book, but I’ve heard good things.
A fairly useful free dictionary app is kanji go. It has a few issues (I don’t see a way to copy and paste search results) but is useful if you don’t have internet access. A good online dictionary is here. You can also look up unfamiliar kanji through its radicals on this site (the kanji look-up tab, radical selection method field).
Basically the more you put in, the more you get out. I’m not at the point where I can follow much more than simple phrases in a movie or video, but I think that may be due more to a dearth of vocab than anything else. The first few months will be a little tricky, but it becomes addictive as you keep learning more.
Good luck with it.