Truly unique email addresses and passwords per service is the strongest approach, but there may be alternatives. For instance, Gmail allows address+tag@gmail.co

Truly unique email addresses and passwords per service is the strongest approach, but there may be alternatives. For instance, Gmail allows address+tag@gmail.com, which will save you from the lowest hanging fruit (block the +tag when it’s compromised to prevent the laziest spam from reaching you). iCloud also allows automatically generating a new email address that forwards to your inbox for a new account when using iCloud Keychain (possibly when using other password managers too, but I haven’t tried).