Selectivity in the early season is typically not an issue as water temps remain low and insect hatches remain sparse to non-existent, although sometimes you may encounter an early season midge hatch that gets the fish moving and feeding selectively. What pattern you fish is generally a secondary concern to location - where the fish are feeding, which is usually oportunistically. A wide variety of patterns can be successful, especially those which are suggestive and could resemble any of of a number of food sources that trout normally would recognize in a given body of water, especially early season food sources like scuds, leeches, dragonfly nymphs, immature damsels,chironomid larvae (bloodworms) etc.
With that, Gary's suggestions cover those "meat and potatoes" food sources that trout will be looking for in the early season when feeding opportunistically, and, in the case of a midge hatch that leads to selective feeding, small and black is usually a good place to start, adjusting color and size as needed to "match the hatch". Micro leeches (12-16) are a "go to fly" when fishing the warmer, shallow water, as are chrironomid larvae (bloodworms) which move from their deep water haunts of winter to the shallower, warmer water where they are easy prey for the trout.
Rickard's Stillwater nymphs, large "chromies", and Bionic worms are three patterns I would add to the list. If I was fishing a lake where the primary food sources where minnows, shiners, etc.. I would fish larger baitfish types of patterns (large clousers, articulated leeches, etc.)