Things you put in your calendar have a much higher chance to get done. You will receive reminders, your smartphone will show you your events, etc... they will be hard to ignore.
When you realize that, you will start blocking time in your calendar for the things that matter most, even if they don't have a particular deadline.
Don't overschedule. When people discover the power of putting things in the calendar, they tend to go overboard and try to schedule everything down to the minute. This can add more stress because plans change and you will feel frustrated that the plan you have scheduled rarely come to fruition.
We believe there is a middle way. Schedule the tasks that are most important and that you are likely to forget or resist doing.