To design OOP data structures in C++, you need to follow some basic principles and steps. First, you need to identify the problem domain and the data requirements. What kind of data do you need to store and manipulate? What are the operations and constraints on the data? How will the data be accessed and modified? Second, you need to define the classes and their relationships. What are the main entities and concepts in your problem domain? How do they relate to each other? What are their attributes and methods? How can you use inheritance, composition, and polymorphism to create a logical and flexible class hierarchy? Third, you need to implement the classes and their methods using C++ syntax and features. How do you declare and define classes, constructors, destructors, access modifiers, operators, and virtual functions in C++? How do you use pointers, references, dynamic memory allocation, and templates to manage memory and data types in C++?