Step 1, have fun and imagine the things you can do once you gain a certain proficiency in Japanese.
Like most have said you need to pace yourself and also enjoy it. There was a period of about 3 months, when I was pretty sick.
This was due to review after review (not so much Wanikani mostly Memrise [at the time]). It got soo bad, within that three month period, all i was doing in memrise and wanikani - no other study. The amount of reviews daily was coming to high hundreds per day. In addition I had work for 8-9h per day (travelling included). My head was going all weird, felt strained and I was forgetting everything. Eventually, I binned of memrise and was just doing wanikani, which also sufferred badly all my enlightened and master was coming in and most were falling back to apprentice. This was massively depressing. This is why I was on level 9 so long - even know i never give up wanikani, i did with everything else. Now I try keep my queue around 100 review. This allows me to do wanikani, grammer study, kitsun[vocab[own deck]/genki[community]/katakana4.5[community].
In addition to pacing yourself, another huge thing is sleep. I feel plenty of sleep is required for study. There a days, where I feel like a studied too much and my mind is too strected. Nothing sticking or making sense. I would read a grammer point or soemthing and its just not making sense. Go to sleep decent amount of time and go back and the point I was trying the previous days clicks and makes sense. I should also note, when i came out of my 3month period borderline burnout, i slept like 18 hours, and I have never slept that much, I mostly stuggle to get 7 hours sleep per night. It really shocked me, but i guess my body needed it.
Another reason, remind yourself why you learning. I initially started Learning Japanese, is because i always said I was crap at languages, so I set myself a challenge. Why japanese, I didnt want to learn one that uses the alpabet and I guess something interested me about japan - even if i didnt know what per say. How does this help? I set myself a goal to learn a language and I am stubborn, i’ve invexted too much, cant quit now…
Now one day I would like to be able to watch Movies (without subtitles), Podcasts and Read literature in Japanese. I already watch movies with subtitles (and while i may not get most of what being said, i kind of grab the gist of the story), also feels good when you do understand something, count your small victories like that… its important.
 I should also note, I only spend about 1-2 hours on study as I do have work and even that can feel too much, for new grammer I seem to study that more at weekends where I do have more time, but i try do bunpro daily…