One page, one observation
A notebook becomes easier to keep when a page has a small task. Instead of summarising an entire day, choose one thing: the shape of a shadow, a sound from an open window or a new leaf on a familiar tree.
Write a concrete sentence before adding an explanation. Describe the colour, position or movement first. If a sketch helps, draw only the relationship you want to remember, not every object in the scene. An arrow and a few lines can be enough.
End with a question worth returning to. Does the same shadow reach the doorway tomorrow? Does the street sound different in rain? A useful notebook leaves a reason for another walk.