I’m one of those people with a public study log in the forum, so I don’t know how relevant my advice is for you, haha, but I’ll try anyway 
My biggest tip is to write about things that are interesting to you during your studies. I have a whole section in my log where I just write about fun encounters with Japanese outside of active studying, because I do a lot of passive immersion. So I write about moments where I could understand something new or unexpected to me, or moments where I encountered a WK word on twitter or in a wrestling promo, that sort of thing.
I doubt this information is relevant to the interests of many others on this forum (though I try to include enough context that it at least makes sense), so it’s mostly just there for me, but I find it really helpful to look back at these posts and see what I’ve accomplished in the time that I’ve been studying. It also helps me synthesize my knowledge and remember things better if I write about them.
I also don’t keep a daily or weekly log, and instead post updates tied to my WK progress. So I’ll publish a new log entry whenever I level up (roughly once every two weeks). I realized pretty early on that making these posts had become sort of a reward for leveling up for me, so I do them partially as an incentive to keep going. I’ll add to the post draft slowly over the course of a couple weeks, and there are always new and exciting things I want to share, but I have to level up if I want to share them!
I think the big thing with language learning is you have to find a way to let the small victories sustain you. You have to find ways to enjoy the hard, slow beginning, where it feels like you’re putting in so much work and not getting substantially closer to reaching your actual real goals.
I personally haven’t had much luck with to-do lists helping much with motivation. I also keep one every day for language learning tasks, though it’s in a physical planner and not online anywhere. Sometimes keeping a to-do list helps me complete an individual task that I otherwise might’ve been lazy about (if I checked all of the other boxes but hadn’t done any reading that day, for example, it might motivate me to read at least one page of manga so that I could check every single box), but if I didn’t genuinely really enjoy the process of language learning itself, I doubt the to-do list would be enough to change that. My study log has been much better motivation for me.
You can look at my study log and see for yourself what the layout of it looks like, haha, but the main sections I have in it are:
- Section at the beginning where I briefly talk about what the WK level and the past two weeks were like for me
- Section on fun encounters with Japanese outside of WK
- Section on the lesson(s) I worked on in my textbook, Minna no Nihongo, over the past couple weeks
- Section on reading/active immersion
- Section on any new resources I discovered, sometimes with a follow-up section on new WK scripts
- And finally, a section at the very end where I talk about my plans for the next level, and sometimes talk about something that is beyond my ability right now, but which I would like to revisit in the future
I’ve experimented with tracking the time I spend on my studies and that sort of thing, and it was helpful to do it a few times just to get a ballpark estimate, but ultimately tracking the time was itself a waste of time, so I forced myself to quit doing it .
I did work to establish a daily routine pretty early on with both WK and my textbook (my study log details both of these lol), and I have a routine with reading currently because I’ve been following along with the absolute beginners book club here.
Having routines definitely helps me accomplish my tasks every day, especially when I’m trying to balance so many types of studying at once. But having the study log really helps keep me accountable because I try to report on all of the different things I’ve been working on, and I feel guilty if I haven’t been reading anything, for example.
I also like my log being public on the forum because occasionally people will reply to my posts and talk about some of the things I mentioned, or offer me advice, or help with some of the Japanese questions I had, or just post general encouragement. I think staying connected to a community of language learners really helps keep me motivated, too, because I want to succeed so that I won’t let down the people who have been following my journey.