The CCIE R&S is an expert level exam, and we will not find per example a book that has all of the information you need in order to pass this exam. One way to help building the knowledge foundation for the exam comes from your real-world experience. As you get more exposure to the technologies, the more confidence you build.
A proper study plan should have a mix of reading, taking courses, and hands-on experience. Yes, we are talking about the CCIE R&S written exam, but believe me:t hands-on experience or practice helps to build the knowledge and retain the theoretical concepts you gather from reading and courses.
When I took the exam, we did not have available CCNA and CCNP exams. While there is no pre-requisites or mandatory path to take the CCIE R&S exam, I’d recommend taking these exams since they also help as preparation path.
Have a plan for when you want to take the exam that will accommodate a realistic studying time based in your workload and personal schedule. For some, a 6-month plan works, for others more time may be needed. Consider having check points or milestones in your plan. As the exam date approaches it is a good idea to slow down you study.
Start by reading the books like exam specific guides expanding to more specific books or technical literature as needed. One example is when you want to explore or focus in OSPF routing protocol. As I mentioned earlier, I find that adding some hands-on practice will help build the foundation. Configuring the different types of OSPF Autonomous System on real routers or observing the transition from Spanning-Tree protocol state to another on a real switch are some examples.