I have a clipboard full of plain lined paper.
Every evening I look at my schedule, I look at my Ambleside Online charts, and I think about what else I have planned for the next day.
Then, I quickly write down a checklist of what lessons we will do together as a family, and little checklists of what lessons I will do with each child individually.
And that's all there is to it! Ten minutes, tops.
I find that if I'm ever too tired in the evening and skip this step, the next day is practically guaranteed not to go smoothly. I think it's not the list that makes the difference so much as the process of making the list. Making the list helps me mentally walk through my day before I find myself in the middle of it.