Your to-do list is your enemy; Your calendar is your best friend.
The to-do list is the demand for your time. Anything and everything that is seeking your attention goes on that list. But who is checking this demand vs the supply of your time?
If your to-do list has 20 items, who is helping you check if you actually have time for all those items? And how are you prioritising the ‘big rocks’ first and the ‘urgent but not important’ busy items later?
That’s why, your calendar is your best friend. Start every morning by planning your day and adding your big rocks to your calendar. The less important items will automatically fall off (they will have no place to go!). Demand for time will meet supply of time (always limited, only 24 hours), and then you can focus purely on execution.
Plan (list and prioritise), Calendarise, Reflect, Repeat.