Use compact loops for dv/dt and di/dt circuit paths (power loops and gate drives)
Use minimal, yet thermally adequate, copper areas for heat sinking of components tied to switching nodes (minimize exposed radiating surface). Hide copper associated with switching nodes under shielded magnetics, where possible
Use copper ground planes (possible stitching) and top-layer copper floods (surround circuitry with ground floods)
Use a 4-layer PCB, if economically feasible (for better grounding)
Minimize the amount of copper area associated with input traces (to minimize radiated pickup)
Heat sink the quiet side of components instead of the switching side, where possible (like the output side of inductor)
Use Bob Smith terminations, Bob Smith EFT capacitor, and Bob Smith plane. Use Bob Smith plane as a ground shield on input side of PCB (creating a phantom or literal earth ground)
Use LC filter at DC-to-DC input
Dampen high-frequency ringing on all switching nodes, if present (allow for possible snubbers)
Control rise times with gate-drive resistors and possibly snubbers
Switching frequency considerations
Use of EMI bridge capacitor across isolation boundary (isolated topologies)
Observe the polarity dot on inductors (embed noisy end)
Use of ferrite beads on input (allow for possible use of beads or 0-Ω resistors)
Maintain physical separation between input-related circuitry and power circuitry (use ferrite beads as boundary line)
Balance efficiency versus acceptable noise margin
Possible use of common-mode inductors
Possible use of integrated RJ-45 jacks (shielded with internal transformer and Bob Smith terminations)