Hang something small and near on the task. No coffee until the expense form is in. Not a treat later in the month, something you actually want in the next ten minutes.

Whatever the record is, do it the same day, every time. The salesman writes his notes in the car outside the client's office. Not that evening, not on Friday.

Putting tomorrow's envelope beside your keys only works if the keys are the only other thing there. On a counter covered in post, the envelope just becomes part of the pile.

Letting the natural consequence do the teaching only works if it arrives soon enough to be connected to what you did. Where the gap is months or years, nobody learns from it. Not you, not anyone.