Move heat into copper
Wide traces, copper areas and thermal vias reduce the thermal resistance from junction to board. The copper weight and via count are set by the power dissipation, not by aesthetics.
Place for airflow
Hot parts on the windward side, temperature-sensitive parts away. Keep tall components from shadowing the hot ones.
Check with measurement
Run the prototype at rated load and measure with a thermal camera. A design that is comfortable on the bench can be marginal inside a sealed housing.
