Clarity comes first. Labels should use the user's words, icons should be recognisable or labelled, and every screen should make its purpose obvious. If people have to guess, the design is not finished.
Consistency reduces learning. When buttons, spacing, wording and behaviour are the same across the product, people learn once and reuse that knowledge. A design system is the usual way to keep this.
Visual hierarchy guides attention. Size, weight, colour, position and space tell people what matters most and what to do next. A screen with five equally loud buttons has no hierarchy.
Feedback confirms actions. Pressing a button, saving a form or dragging an item should get an immediate, visible response. Small, purposeful motion is one of the clearest kinds of feedback, as long as it is quick and respects reduced-motion settings.
Accessibility and forgiveness complete the list. Good contrast, readable text, keyboard support and clear focus states make the interface usable for more people. Confirmation for destructive actions and easy undo make it safe to explore. Simplicity ties everything together: remove what does not help the user reach their goal.