How do I set default notifications for tasks and appointments?

When you create the appointment, you can choose a reminder option under the reminder section.

You can also set this as a default option which will apply to any new appointment you create. To do this, choose Daylite > Preferences > Notifications > Appointments. Then select Message with Sound from the little drop down options.

Check the boxes to apply default reminders to new tasks and appointments you create and to received items through delegation or invitation.