Establishing a set of design principles for a project or brand can help teams create more consistent user experiences. They aid decision-making and make it easier to keep the product aligned. If you plan to establish a set of design principles for your product, we came across useful resources that will help you get started.
Ben Brignell curates an open-source collection of 195 design principles and methods. It features both heuristic design principles and design principles developed by companies specifically for their products. All of them are searchable and tagged, from hardware and infrastructure to language and organizations.