The following article has examples of common registration rules and the conditions you should add to create them.
This rule enables you to deny all registrations except those from people who belong to a particular organisation.
Initial Screen

Choose which options the rule should be applied to

Add ALLOW rule

Deny Message

This rule enables you to deny all registrations except those from people who are a member or have a certain membership type.
Initial Screen

Choose which options the rule should be applied to

Add ALLOW rule

Deny Message

This rule enables you to deny a person from registering for a course if they have already registered for the same course on a different date.
Initial Screen

Choose which options the rule should be applied to

Add DENY rule

This rule enables you to deny a person from registering for a course if they have not purchased a ticket (optional extra).
For this method to work, the course must have no price. Only the tickets (optional extras) should carry a price.
Initial Screen

Choose which options the rule should be applied to

Add DENY rule
This rule enables you to deny a person from registering for a course if they are using an email address with a public email domain (e.g. forces them to use a work email address).
Initial Screen

Choose which options the rule should be applied to

Add ALLOW rule

If you want to only allow personal email addresses to be used, you can also use the same rule but with is public email domain.