1. Determine what is your system you need to design.
2. Determine the requirements and goals of the system, such as functional requirements, non-functional requirements, and extended requirements.
3. Estimate the traffic, storage, bandwidth, and memory.
4. Definite some APIs.
5. Based on the estimation of the traffic, determine the database schema, such as the database table.
6. Determine high-level schema design.
7. Based on the high-level schema, focus on a certain component.
8. Consider non-functional requirements, add load balance and cache, and DB cleanup.