Design principles are what UX/UI designers use intentionally or subconsciously in their day-to-day workflow. These are the fundamental rules that help achieve great results in the visual, user interface, graphic, or any other kind of design. These rules are based on the Gestalt principles created by psychologists in the early 20th century in Austria and Germany.
Design Principles in UI
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Make sure you evaluate your designs against each of these principles and achieve a good combination of them in your composition.