Melissa Raffoni writes: To-do lists will be only marginally useful if you don’t set parameters for how much time to devote to each task. When you make your list, carefully estimate the time each task will take, and box it into your calendar.
This discipline not only will help you finish your list, but it also will improve your ability to estimate time and manage expectations of those around you. Particularly if you are in a new position or are confronting new tasks, ask for help estimating the time for each task—otherwise, you run the risk of missing deadlines and mismanaging expectations. Link.