SRE is a specialized software engineering discipline, the sort of thing you'd do if you had a team of 20 SWEs and wanted to write something like Kubernetes or Puppet. Good books on SRE (besides the Google book that popularized it) cover UNIX and Linux operating system concepts, low-level networking, and software architecture in general.
On the other hand, if you've got a team that does a lot of operations work by hand -- runbooks, MOPs, checklists, etc -- and want to automate it, then you should be looking for books on modern systems administration. Look for references to specific technologies such as Kubernetes (or Mesos), Terraform (or CloudFormation, or Pulumi), Puppet (or Ansible).
(context: I've been an SRE for ~10 years, first at Google then Stripe)
You need to synergize different tools such as Terraform to implement the principles
This is DevOps maturity model called DORA: https://sre.google/ Check out CNCF on tooling: https://sre.google/
Useful short reading: https://sre.google/ but make sure you read Site Reliability Workbook... first.
https://www.amazon.com/Site-Reliability-Workbook-Practical-I...
Also you'll see ITIL framework, its usually horribly overweight if you're small or even medium sized, but might give you some ideas.