The summary.
PROXIMITY IS THE STRONGEST GROUPING SIGNAL
Things near each other are read as related regardless of anything else. A label must be closer to its own field than to the one above.
Use a small scale of spacing values rather than arbitrary ones.
DECIDE WHAT SHOULD BE NOTICED FIRST
If everything is emphasised, nothing is. One primary action per screen.
Squint at the page: if what stands out is not what matters, the hierarchy is wrong.
ALMOST-ALIGNED IS WORSE THAN CLEARLY DIFFERENT
Two elements nearly aligned read as a mistake.
LABEL BUTTONS WITH THE ACTION THEY PERFORM
"Delete account", not "Confirm". People read the buttons, not the surrounding text.
EVERY ACTION NEEDS VISIBLE FEEDBACK
Without it people repeat the action or assume it failed. Beyond a second, show progress.
THE STATE MOST OFTEN MISSING
Focus. Never remove the indicator without replacing it — keyboard users then cannot tell where they are.
RIGHT-ALIGN NUMBERS
They can then be compared at a glance.
MOTION SHOULD EXPLAIN, NOT DECORATE
Keep it short, and honour the reduce-motion preference — motion causes genuine discomfort for some people.
SPEED IS EXPERIENCED BEFORE THE DESIGN
Avoid layout that shifts as content loads; it makes people click the wrong thing.
