For homework and bills, I suggest a bullet journal, digital or analog (physical journal works best for me. Record due dates not only on the day they are due, but a week, then 3-4 days before and finally the day before. If you don't need as many reminders as I do, then don't put in as many.

For academic work I get the syllabus at the start if each class and work out small, easily digestible increments and set due dates for those during the course.

Ex. One chapter a week is assigned reading so I divide the chapter over 4 days. I build in wiggle room in case life happens which is why I divide over 4 days instead of seven.

Ex. For papers that are due a month out I divide into three weeks: week 1 for research, 2-3 for writing (sometimes I end up needing more research once I start writing, week 3 for outside review and editing (or week 4 if I had to do additional research).

If I find that one day or week is really heavy with tasks I adjust as needed. This may seem pretty involved, but I was able to keep up with schoolwork while suffering a health crisis. I didn't need any extensions on assignments due to planning at the beginning if the classes and a bit of luck.

For everything else like sleep and fitness, schedule it like anything else. But these are things you may want to try to be more strict in terms if when you do them. Sleep schedule should be more regimented in terms of times than an activity like fitness.