Ben Shneiderman introduced the 7 Golden Rules of UI in his book Designing the User Interface, and they've held up surprisingly well. They're not abstract theory. They're practical, and you can feel when a product violates them.

Rule 1: Strive for consistency. Use the same colors, type, buttons, and interaction patterns throughout. When things behave predictably, users stop thinking about the interface and start thinking about what they actually want to do. Design systems exist largely to enforce this.

Rule 2: Enable shortcuts for frequent users. Beginners need guardrails. Experts need speed. Keyboard shortcuts, gestures, and quick-access menus let power users move fast without making the interface hostile to newcomers.

Rule 3: Offer informative feedback. Every action should get a response. A loading spinner, a success message, an error notice. Silence is confusing. Users need to know the system heard them.

Rule 4: Design for closure. Tasks should have a clear end. Confirmation screens and completion messages aren't just nice to have. They tell users "you're done, you can relax now." That psychological signal matters more than most designers realize.

Rule 5: Prevent and handle errors. The best error message is no error message, because the interface stopped the mistake from happening. Input validation, smart defaults, and clear constraints do that work. When errors still happen, recovery should be obvious and painless.

Rule 6: Permit easy reversal. Undo is underrated. When users know they can reverse a mistake, they explore more freely. Fear of breaking things makes people timid and frustrated.

Rule 7: Support internal locus of control. Users should drive the interface, not the other way around. Unexpected pop-ups, auto-redirects, and actions that ignore user intent all erode trust fast.