My philosophy of grounding is to flood every possible mm² with ground copper and then connect all the grounds with many thru-hole vias. This makes the impedance of the grounds as low as possible. If you have high current areas, isolate the ground return path with "herding" cuts in all the ground coming from that area to the main ground connection. A herding cut is simply a thin (~0.010") cut in the ground plane, creating a "star" grounding scheme. If you have multiple layers with ground, and you should, don't place the cuts right on top of each other, but stagger them by 0.050" or so.