I'd recommend starting with the Japanese Pronunciation Trainer, then tackling the Kanji radicals (https://fluent-forever.com/japanese-radical-deck/ ), and then learning from the 625 wordlist [learning the Kanji for each word as you go, and using Kanji signatures and additional mnemonics as needed, as per https://fluent-forever.com/kanjisignatures/ ). As soon as you feel somewhat comfortable creating simple flashcards for the words in the wordlist (perhaps after 30-50 words), then I'd suggest moving over to full sentences, as per https://fluent-forever.com/hacking-fluent-forever/ - It'll aid in retention, and for Japanese, you'll want any help you can get when it comes to retention!
Also, in hindsight, I'd recommend creating mnemonics extremely often for Japanese. Do it 100% of the time you encounter a new radical, and if I had it to do over again, I'd do it 90-100% of the time I saw two radicals combined together. They don't take long to create, they're extremely easy to memorize, and they make all future flashcards involving that radical combination a lot easier to remember.