The wood out on the "wings" of the body doesn't do very much structurally. For weight reduction, you can hollow them out extensively, making it into a semi-hollow body, if you want.
In the structural zone of the body, which is the area from the neck pocket back to the bridge, the best way to remove weight without significantly weakening it is to cut parallel slots. They should run lengthwise, leaving ribs between them; like routed 3/8" wide slots with 3/8" wide ribs. The best way is to rout them from the inside, if you have a separate top and back, before gluing them together. Or, you can rout them from the top, and cover them over with a thin cap.
Deep crosswise slots, like a deep pickup cavity, are what weaken the body. Cut them sparingly to avoid those pesky on-stage bass implosions.