"Don't reuse email addresses" should become as common advice as "don't reuse passwords."

Buy a domain and set up a catch-all email address, use a unique one for each service. Alternative options exist as well (Apple's "Hide My Email" for ex.)

Don't do the "add a plus sign at the end of your username to create unique addresses" thing. You still have a single point of failure and it causes weird bugs in poorly designed email addresses validation.