You fix a small upper limit to the number of tasks you’ll be working on at any one time – say, three. Then, you add no further tasks to your plate until you’ve finished at least one. When there are only two tasks remaining in your WIP, you can bring in one more. And so on. The kanban system visualises this using Post-its on a whiteboard, arranged in columns: each task moves from the “to do” column to “doing” to “done”. If your WIP limit is three, there should never be more than three notes in “doing”. (You can add a “waiting” column, where you shunt tasks that are waiting on other people.)