First you need a lake with big slabs in it then
I drill holes until I find the school of slabs, Big gills can be found anywhere on a given lake; deep, shallow, suspended. I prefer to fish shallow so I look shallow. Prime areas are weed edges, holes, and structure. Gills can change their pattern in the blink of an eye. When you find a school of little ones in weeds, drill the area out throughly the big boys may be close by.
-Scott