I have a workflow that assigns a task to a person. I need to set up alerts so that this person would get daily reminders to complete the task starting 3 days before the due date.
If the due dates never change, you can add steps to your task-initiating workflow to calculate the day that is 3 days before the due date, then pause until that date, then send the reminder email, then pause 24 hours, then send the second reminder, then pause 24 hours, then send the last reminder.
If your due dates might change or if you want the reminder emails to continue forever until a task is approved, you need to create a timer job to run your workflow. It's not recommended, but you can hack together a solution using the two on modified workflows trick on your task list: create two different workflows that run when an item is created or modified, add a "pause for 24 hours" delay to one of them, and have them both modify a minor aspect of the list item.