Start with the surface. After a big overnight hatch, trout mooch across the lake and take a small wet drawn past the nose, or a larger dry, sometimes with a nymph under it. Bobs Bits in sizes 12 to 16 is listed for browns and rainbows.
Where fish are feeding on midge, a fly that stands out from the naturals, a large Chernobyl Ant or a Bruisers Bug, is described as one of the most effective ways to get a take. In our experience the trick is to cast to a rising fish, then be patient and let the fly sit.
On the days the surface is blank, wet-fly prospecting along the edges is the sensible fallback.