So, for what it's worth:
I've been slacking massively on kanji study recently, mostly because it's a lot more boring to use flashcards than to read or chat with my friends, so my writing ability has been stagnant despite my reading ability improving greatly.
But this is a method that I've found works well if you can stick to it (with the caveat that I wasn't able to personally): flash cards. What I did was I had several groups of flash cards that I reviewed at different frequencies, and when I did review them, I would write them in a notebook or something. Then I would put them in whatever stack I thought was appropriate for how well I knew them. (This is what you call "spaced repetition".)
I decided to buy some of those flashcards-on-metal-rings (whatever you call them) a couple days ago so I could start practicing writing kanji again, but I'm planning on doing it a little different this time to hopefully make it less cumbersome so I can stick to it:
1. Instead of individual kanji, I'm studying specific words, kind of like spelling. On the front I've got a short sentence using the word with only hiragana/katakana for context (so e.g. I know the card is about 科学 and not 化学), and on the back I've got the full spelling of the word with kanji.
2. I'm adding words on a ad-hoc basis, where I see or use a word and think, hey, I can learn that kanji. E.g. 覚える and 最近 are some of the first ones I'm putting on there in my case.
3. (this is important) I'm only putting in kanji I'm struggling with or that are completely new to me, and the plan is to take them completely out of the stack when I feel comfortable writing them for a couple months or so. This is going to lead to forgetting how to write quite a few kanji I imagine, but I'm hoping this will take away the monotony of studying well-learned words that I just don't use much, like 助ける.
4. I'm using long intervals. No daily review kanji, just weekly and monthly, I think.
Again, this is something I just started, so I don't even know if it will work or not, but just sharing in case you find it useful. The important thing is that you find a routine that works for you; it needs to be something you don't dread doing, most importantly (preferably something rewarding if possible, though that's going to be tough with writing practice).
Also, I would recommend at least some writing practice; even if you aren't too worried about being able to handwrite kanji like a pro (which is a skill falling even for native Japanese people IIUC), writing a kanji a bit helps solidify your understanding of it. Sometimes kanji, especially the really complicated ones, can look like blobs of ink, but if you know how to write them then you'll see more clearly that e.g. 葉 is a stack of 草世木, or that 難 is like the right half of 漢 with the bottom-right half of 曜.
If a kanji is really confusing, you might also consider looking its etymology up here:
And FWIW this is my typical stop for finding the stroke order of a kanji (though there are of course tons of sources for that):
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