I think I need to create an scheduled rule that checks daily if a ticket's Due Date is near, and then send a notification to the Assignee if it's within range.

Problem is, I'm not very well versed in JQL and I'd like to learn how to write this query in it. Thanks!
It needs to notify the assignee if their due date is less than 4 days away, and/or when it's overdue.
If (DueDate - TodaysDate) < 4, then notify Assignee