Set up your assignment reminder rules by clicking on Assignment reminder rules link on the Setup panel.
Add new rules by clicking on the Add assignment reminder link, right-click on an existing rule to edit, delete it, or move it up and down on the list. Remember that the rules here are processed in order, so the higher rules on the list (lower numbered) get run before the lower-priority rules.
Operations
The rules for sending assignment reminders are followed in priority order, one after the next. If a rule which matches the current situation is found, the actions within it are taken:
Why "none of these"? If you don't want your senior volunteers pestered by reminders (they're always the most reliable, right?), you can define a high-priority rule which matches them by person type or group, has Send notifications set to No reminder notifications, and If this rule applies... un-checked. This has the effect of matching those volunteers, doing nothing to remind them, but allowing other volunteers - which didn't meet these rules - be notified as they match other, later rules.