Protect Your Ground Planes
For all the good a ground plane can do, it can also act as a direct path to your sensitive components if an ESD pulse discharges directly into it. To prevent this sort of damage, remember to use TVS circuits between the power and ground on sensitive components to divert the induced currents. When implemented correctly, the voltage differential experienced by components will be held to the clamping voltage of the TVS.
You can also use high-frequency bypass capacitors between power and ground on sensitive components. The capacitors will reduce the charge injection and voltage differences between power and ground. Keep those capacitors and your TVS close to the components you are worried about protecting.
Additionally, you should use a copper land when you are attaching connectors to your PCB. Make sure the land is separate from the PCB ground, or you just introduced a nice, low resistance path for ESD to reach all your components, even though you put all that other protection in place. And, in general, you should minimize path lengths whenever you can.