Carp will take all manner of flies depending on the availability of food sources. At times dry flies imitating mayflies or midges or terrestrials are the ticket. Other times it's subsurface patterns including streamers, nymphs and crustaceans (crayfish, scuds, snails etc). Day-in and day-out the last category is the most consistent producer. Why? Carp are opportunistic feeders and won't pass up an easy meal when feeding on the bottom.
The best flies are sparse, simply tied and usually about 1 inch to 1 3/4 inches long. Most are weighted, but only slightly (they need to sink, but land in the water quietly). Use lighter weight flies when sight casting to carp on shallow flats in lakes and reservoirs; one weighing from .2 grams up to .5 grams. In deep water off rip-rap or in creeks and rivers with moving water use a slightly heavier fly; something weighing from .8 grams to even a full gram.
Many excellent patterns are tied so that the hook point rides up to minimize snags and facilitate hookups. The most affective colors are black, dark olive, brown or rusty brown. The productivity of these patterns is not in painstaking detail, but in the liveliness, or animation. Simply stated, these flies work because they trigger a feeding response. Above all other things, confidence is key! This is true for both fly choice and technique. Only if you have confidence in your fly will you be persistent, and you have to be persistent. Put your fly in front of as many fish as you can. In a typical day of carp fishing you will cast to many uninterested fish. This may not mean that you are doing something terribly wrong…it means carp are a challenge.
Favorite Stillwater flies are the “Backstabber Carp Fly”, “Carp Slider”, “Clouser Swimming Nymph” and the “Half-Back Nymph” Top flies for rivers are the “Belly Crawl” and “Near “Nuff Crayfish”.