1. I'd say get started on hiragana and katakana ASAP but you already seem to have those down so yay, that's like half the text you'll be reading around!
2. Try to use as little English and as much Japanese as possible. Pretend you don't even speak English anymore and the only language you have to learn and communicate (and think and dream) with is Japanese. seriously it helps, especially if you surround yourself with Japanese native speakers and media/music all day, everyday.
3. Dive straight into kanji and don't get intimidated and leave it for later. Once you start memorizing and linking them with mnemonics you'll get addicted. Bushu (radicals) are your best friends here. they're the parts that make up kanji characters (kind of like how letters, rather than random individual strokes, make up words) and even when you come across kanji you don't know, you may be able to guess its meaning by the bushu that make it up.
(kanji may not be essential for ~N5 JLPT exams since I noticed they provide furigana readings for them but they'll still help you learn the meaning of words if their pronunciation fails you)
4. Listen, don't just read, since a third of the JLPT exam requires listening skills and many people neglect that. Youtube channels/podcasts like Japanesepod101 are great for that.
5. If you like using apps, the best I've found so far is Kanji Study by Chase Colburn since it combines everything any other app has and more. Only the first level N5 and the very basics like kana sections are free and if you want to advance you'll have to pay but it's totally worth it.
That's how I get by at least. I'd hate to throw platitudes at you but honestly, regular, consistent practice and repetition are key so you improve without burning yourself out by trying to learn too much too quickly.
Would love to know other tips from advanced learners. The articles here were extremely helpful and encouraging too when things get overwhelming.