. You need grammar, vocab, and experience.
For grammar you might want to grab Tae Kim's grammar guide. It's free, cuts to the chase, and doesn't treat you like a toddler. You don't want to actually memorize it though; just read it. Carefully. It's going to give you a good enough starting point to start up on native material. Once you start reading / watching in Japanese and encounter a grammar structure that doesn't make sense to you, look it up on imabi or DoJG. Having experienced the process of learning a few languages, all I can say is: it's exposure that counts. Long-winded explanations of grammar structures and countless exercises for drilling them into you head just don't work really well. Get the basic idea of grammar, and go consume native material. When you're utterly unable to figure out the meaning of what you read / heard, refer back to a grammar resource. JP grammar is kinda scary at first, but it's still much easier than its English counterpart.
Vocabulary. There are two common approaches: learning kanji in isolation via an RTK Anki deck combined with (or followed by, if you can't handle the time investment) a good core deck. Core decks use frequency lists to pinpoint most common vocabulary and have you up and running as soon as possible. There are quite a few those (of extremely varying quality), and you choose one that suits your needs the most. This approach makes sure that you first learn to recognize 2000+ kanji by their keywords in ~2-3 months, so that you'll have easier time learning vocab by applying mnemonics. For instance: 大人 means an adult. You can memorize it as is... or, with prior knowledge of kanji and their "general meaning", you can create a story: 大 means large and 人 means person. Add them together and you've got "large person" = "adult". This example is super simple, but there are lots of difficult kanji and words that become so much easier to memorize by using mnemonics. The downside of this approach is: you need to complete an additional deck for isolated kanji study that will take you... well, about 2-3 months at 60-90 minutes a day. The other approach is to ignore isolated kanji study, and focus on vocab from the get-go. Yes, 曜 might look like a complicated kanji, but you'll be seeing it so much, you'll eventually remember it. The same applies to all kanji. You do a vocab deck, and just memorize kanji as they show up. Whether this method is more or less efficient depends heavily on you. The debate on isolate kanji study vs kanji through vocab has spanned long years now, and no consensus has ever been reached. I had huge issues memorizing kanji through vocab, so I did an RTK deck alongside a core one. Your mileage may vary. As always.
Experience is the fun, and initially super frustrating part. You take your flimsy understanding of grammar and patchy database of a thousand or three words, and start consuming native material. Starting with simpler things that still engage you. The single best resource to use at this point are visual novels. Not everyone's cuppa, clearly, but they're a perfect fit for the purpose. They combine text, audio, and visual cues. So ideally, you want to read one or two visual novels, and look up every grammar bit you don't get, make an anki card of every new word you come across (with audio, which is super simple with vns), and get your brain used to processing Japanese. Afterwards just read / watch whatever you want. And preferably continue making new cards out of all new things you come across.
Japanese TV is a bit tricky, to be honest. While you'll be able to get the general gist of what's happening pretty easily, the majority of references, jokes, kanji puns, and so forth will be obscured from your understanding. Initially, of course. With time, bumps and lows will even themselves out.
So, a super short summary:
My recommended route for getting you up and running as soon as possible is (1a-c should be done at the same time over the course of ~3 months):
1a. read Tae Kim's grammar guide to get basic understanding of Japanese grammar
1b. (optional) do a "Remembering the Kanji" (RTK) Anki deck
1c. do a relatively short core deck (if you plan on doing the next step, then the 'core 2.3k vn order' deck will be a perfect match, otherwise just use Core2k)
2 (optional) read one or two simpler visual novels and make new anki cards of whatever unfamiliar words / grammar structures you come across
3 consume any native material that you're interested in, and make new anki cards of whatever unfamiliar words / grammar structures you come across for the rest of your life
Assuming you do all of the above, you should be able to watch unsubbed TV within about a year. And understand most of it within 2 years. This method is highly dependent on your memory and time input. It's also rather time consuming, as just Anki cards may well peak at about 2-2.5 hours a day.
But by investing about 3-4 hours a day, you too can watch unsubbed anime