A few of mine spring to mind:
- Fat power tracks, especially ground. Use ground fills over the entire pcb so that ground occupies all otherwise unused space. Note that fills dont have to be solid to be effective - I use hatched fills these days. Spend time on the board bunching up non-power tracks so that the ground can be wider ie consolidate unused space so that it can become part of the ground fill.
- Decoupling capacitors on everything, ideally as close as possible to the power pin of the device they’re decoupling ie so close their courtyards nearly create a violation. I place them next to the power pin rather than the ground pin because the ground fills constructed per item #1 above mean ground is lower impedance than the power.
- Keep switchmode loops small and keep them isolated so that they dont leak. They should connect to the rest of the system at one point, usually the main switchmode input and output capacitor/s. The area of the loops should be minimised. This is usually detailed in the switchmode IC data sheet, disregard it at your peril. I find placing a switchmode supply in a corner of the pcb makes it easier to isolate the loops.
YMMV.
David