ARIN, RIPE and APNIC publish a great deal of useful documentation on how to set up BGP stuff properly in the modern era. And information for how to fully implement dual stack with ipv6.

As for other current best practices there's really a very great variety of disciplines involved in ISP operations, depending on what type of ISP it is. What's relevant for a GPON FTTH last mile provider might not be as relevant for a colocation/dedicated server ISP. Or for a WISP. My recommendation on that would be to pick the subject to research and make inquiries in the special interest groups dedicated to that (for instance, two way satellite, or automated billing/provisioning systems for hosting companies, or CRM systems, or whatever).