When building apps with scale in mind, it's essential to consider key factors such as architecture design, system scalability, database scaling, asynchronous processing, performance optimization, fault tolerance, and redundancy. A modular and scalable architecture, using patterns like MVC or microservices, allows for independent scaling of components without affecting the entire app. Horizontal scaling, load balancing, clustering, and containerization enable rapid deployment and distribution of resources to handle increased user demand. Database scalability is critical, with distributed databases, sharding, caching mechanisms, and asynchronous processing helping to boost performance. Asynchronous processing, message queues, background processing, performance optimization, fault tolerance, and redundancy mechanisms are also crucial for building robust and scalable applications that can adapt to growing requirements and provide a seamless user experience.