A simple and often overlooked pattern is the soft hackle fly. It is incredibly versatile. It looks like nothing in particular, but a great many things in general.
And it can be fished upstream or down; dead drift or on the swing; solo or as par of a tandem rig; just under the surface or with weight.
Last fall on the Esopus I "matched" a late mayfly hatch with this Plain Jane soft hackle fly. As you can see in the photo, the fly got pretty chewed up.
The soft hackle is especially effective at mid-day, in sunlight. It gets fish up out of their comfortable, low-light lairs when nothing else will.