What really helps me is to set concrete and smaller goals along the way to my big, vague goal (which is to be able to watch/read Japanese media in Japanese). At the moment, I work full time and have some other hobbies as well, so my main method of study is renshuu, which is really good for learning vocabulary and kanji, and for getting an introduction in grammar points. I also occasionally watch Japanese dramas (with English subtitles, just so I hear spoken Japanese. But more intense study is not ideal for me at the moment, and I'm fine with that for now. That's another recommendation I have, really look at what you're able to do at this moment in time, and change when circumstances change.
Anyway, at the beginning of this year I set myself 4 goals:
Get to 3000 learned vocabulary on renshuu - quite an arbitrary number, but also one I saw in discussions about fluency. I know that 'fluency' is not something you can objectively measure, but it seemed that with 3000 words, you'll get quite far. Also, it seemed doable for this year, as I had around 2000 I believe. It felt both substantial and achievable.
Get to 600 learned kanji on renshuu - again, achievable and substantial, I believe I was on 400 or thereabouts. I got there already, which gave me a great boost!
Do the N4 grammar lessons on renshuu - this is slightly more tricky, as I don't want to do too many lessons in succession, so I only learn new ones when my grammar schedule looks quite empty. It's a goal I need to push myself on, which is good.
Lastly, to get away from just flashcards, I decided I wanted to play the first case of the first Ace Attorney game in Japanese this year. I already played it in English, a few years ago, so I know it a little. Also, the YouTuber GameGengo did a video explaining every line and every word of the first case (of which I have by now watched about a third). But most importantly, there are some usermade ace attorney vocabulary schedules here on renshuu, so I added the case 1 words to my study regime, generated a kanji schedule based on the vocab, and started studying both. The bigger goal of playing the case has therefore also been split up into very concrete and measurable steps: learn all the vocab, learn all the kanji, watch the video, play (but not immediately after watching the video). The vocab and kanji count for my vocab and kanji goals. The ace attorney case is really where my current memorisation study meets my bigger goal of being able to engage with Japanese media in Japanese (although I'll choose some new goals after I finish these).
All that's to say: think about some concrete and smaller targets that are doable for you, but still offer a bit of a challenge, and make you feel like you're working towards your eventual goal. Whether it's a number of words you'll try to reach, or learning a specific song by heart, or learn vocab and kanji for a specific manga and then read a chapter without using a dictionary, pick one or a few and that might help your motivation!