When selecting computer parts for a build or upgrade, focus on the essential components that will meet your performance needs. Start with a powerful CPU that suits your tasks, paired with a compatible motherboard. Choose enough RAM (typically 8GB to 32GB) to ensure smooth multitasking and consider a GPU if you're into gaming or graphic design. For storage, opt for a combination of SSDs for fast boot times and HDDs for additional space. A reliable power supply unit (PSU) is crucial for stability, while a spacious case with good airflow keeps your components cool. Finally, don't forget peripherals like monitors, keyboards, and mice to complete your setup.