At one point I was working full time, going to school full time, and taking care of my mother. She had a series of strokes that have left her legally blind, with compromised balance, and with dementia. As you can imagine it was a bit insane trying to keep track of deadlines at work, assignment due dates, and mom's appointments/stuff. At the beginning of this year, my sister began to take over mom's care, so I've been able to focus more on school and work.
The thing that has worked the best for me in the past was making a list. Some people make a daily list, but mine is weekly. I've learned that I get overwhelmed with a daily list; the weekly ones tend to give me a feeling of security as opposed to oppression. My biggest rule with the lists was that if it wasn't on the list then it wasn't important enough to stress out about. The other rule was that if someone wanted me to do something or be somewhere they had to tell me at least a week in advance to make sure it ended up on my list.
I'd separate the lists into work, school (mini lists for each class), mom, and personal. It worked really well for me.
Since I currently take classes online, I make sure to take frequent breaks to stretch, go for a walk, or do some cleaning around the house. I'll listen to a lecture, then go for a 15 minute walk. Then I'll do a bit of research before cleaning for 15 minutes. I make sure to always use a timer. I've learned that if I don't, 15 minutes quickly becomes 2 hours and then I haven't gotten anything done.
I do a bunch of other little things as well, but those are the two biggest methods I use to keep from going crazy while making myself a priority.