If you create meetings with busy coworkers, the Outlook Scheduling Assistant should be a part of your process.

With the Scheduling Assistant, Outlook provides necessary information about meeting attendees’ schedules as you’re creating or rescheduling meetings. You will be able to determine the Free, Busy, Tentative, or Out of Office status of the attendees, so you can be sure not to create a meeting when someone is out of the office or when the majority of your attendees are busy.

Remember that this feature is most useful for coworkers in the same organization who keep their Outlook calendars up to date.

To use it, while making appointments, simply click the Scheduling Assistant button in Outlook 2013/2016:

Or the Outlook Web App:

And your attendees’ schedules will be blocked off or not according to their availability.