A blank page can feel strangely public, even when nobody is watching. You imagine the finished drawing, compare it with someone else's work, and decide you cannot begin. A private sketchbook gives that moment a different purpose. The page only has to help you look.
Start with an object close by. A cup is enough. Spend a little time noticing where its edge changes direction, where the handle meets the body, and which side holds the shadow. Draw what you can see rather than the symbol for a cup that your hand already knows.
This is a practical observation exercise, not a test of talent. An uneven line records a decision. A second attempt can record a different one. Keep both instead of judging the first as a failed version of the second.
Research reviewed by Fernandes, Wammes and Meade found that drawing information could improve memory in the learning tasks they studied. That finding concerns remembering information; it does not mean every sketch improves every kind of memory. It does offer a reason to take drawing seriously as a way of working through an idea.
Try a small page divided into three spaces. In the first, draw an object from observation. In the second, write three things you noticed. In the third, draw it again without looking. Compare the pages for information, not attractiveness. What did your attention keep? What did it simplify?
If the page stays private, it still counts. You do not have to post a practice session to justify the time you gave it. Some work is valuable precisely because it lets you learn without presenting a finished version of yourself.
Tomorrow, the same cup will still be ordinary. You may see it a little differently.
Further reading: Fernandes, Wammes and Meade: drawing and memory