I came across this article recently, and it makes sense. How many times have you written out a to-do list only to finish only a few of the items? If you're like me, you do the easy things first, and before you know it, the day is over, and you still have your important tasks not completed. Hopefully, you aren't like me, but if you are, here is a quick summary from the article "Work from a calendar, not a To-Do list." on how to use a calendar instead to complete your important tasks.
Make a list of everything you need to get done in the upcoming week (try to do this before the beginning of the week).
Grab your paper calendar or digital calendar and start plugging in the tasks on days you want to complete them based on how long it will take. Try to be as accurate as possible regarding how long you think the task will take to complete.
For tasks you regularly do each week, write those in for the whole month, especially if it's the same time every week. (I use the Apple calendar and set some tasks on repeat each week or daily).
Color code each task so it's easy to see.
Have a cushion in between tasks, especially for new or complicated tasks.
Get rid of any distractions and only work on one task at a time.
Schedule your most important task when you have the most energy, morning, afternoon, or evening.