An approach to Software Design

• Visualize your system (from inside)
• Identify different (disparate) entities in your system
• Group objects which are inherently common (from functional aspect or in real world aspect)
• Identify inherent relation-ships in those entities: use tools such as is-a, has-a, uses, composition, aggregation, generalization, realization, cardinality
• Identify key data structures to model the entities
• Identify the interaction  model between these entities to achieve the end goal of the system
• Identify tasks and ways you can break down your tasks. 
• Identify task relationships
• Identify Workers or Threads and how and model their interaction
• Choose appropriate Thread Synchronizers in each situation (each has its way of defining a thread interaction mechanism)
• Identify business rules
• Identify actors in your system
• Identify and abstract common design patterns
• Stick to SOLID principles for Design  (Highly cohesive and lowest coupling)
• Ask questions and gather constraints = which are the most essential limiting factors in shaping your system
• Visualize your system (from outside)
• Identify the above things using your system as one component and how it interacts or interfaces with its outside world
• Identify performance goals of your system (latency/throughput)
• Design for performance (scale-able - identify performance/scale-ability bottlenecks): liveness issues/memory leaks/resource leaks issues
• Don't over design
• Start small and let your design evolve
• Keep it flexible and simple (use the SOLID principles of design)