I take extensive notes while I teach, which I then email to my students for their reference throughout the week. (Unpaid endorsement: I use GoodNotes and it's awesome!) Because of this, I don't bother coming up with lesson plans each week for my students. When I first started teaching, I planned out my lessons religiously because I was new and nervous. I was afraid that I wouldn't be able to come up with enough activities to fill a whole lesson. This was useful at first because it made me think deeply about what would help my students to improve in their various weak areas.
But over the years, I discovered that it's best to be able to move in any direction needed while teaching one-on-one. If you have an amazing lesson about dynamics planned, but your student asks you for help with articulation, do you bulldoze their needs that week so you can follow the plan? Of course not. The point of private lessons is to meet individual needs, not to follow a set-in-stone curriculum. This being said, it's essential to include all the basics that every musician needs to be able to do: scales, dynamics, basic music theory, healthy posture, knowledge of the instrument's repertoire, and how to take care of the instrument.
So what I like to do now is to follow my students when they show me a specific need, and when they don't have any pressing issues to address, I take that week to work on one of the aforementioned basics. In this way, they feel heard and helped, and I'm able to give them a well-rounded education so they can go forth and be great musicians.