Refer to dry flies when you talk about the kinds of flies that will float on the water once you cast. These are specifically designed to mimic light-bodied insects that may float on the water when falling into a lake. Materials used include feathers, cork and silicone. Use dry flies when fishing for bass or pike.
Use wet flies when you want the kind of fly that will sink below the water's surface after landing on the water. Anglers swear by these flies when trying to hook salmon in lakes, since these flies adequately imitate a heavy insect that fell into the water and is gradually sinking toward the bottom.
Seek out emergers when fishing for species that eat aquatic insects. Much like dry flies, these emergers stay close to the top of the water--but like wet flies, they sink just beneath the surface. Unlike wet flies, however, they do not sink all the way to the bottom. This is a good fly to use during mosquito-hatching season early in summer and in late spring.
Fish with nymphs when going after trout and also salmon; nymphs mimic the appearance of crustaceans or worms. Nymphs may be weighted down with additional ballast to allow them to sink to the bottom of fast-moving rivers; this is a big plus when going after hard-to-catch fish in waters with heavy vegetation.
Place saltwater flies at the end of your line when you are going after predatory ocean fish that prey on squid, shrimp or small baitfish. These flies sink low, as would be the case with wet flies. As they sink, they actually lure the bigger ocean fish upward to strike.
Attach the fly to the tippet, which is a piece of fishing line that attaches to the leader.
Fasten the leader to the actual fly line. The leader is a lot lighter than the fly line, ensuring that the fly will independently sink or float, depending on its design. A tippet line is sometimes attached to the leader to allow for quick fly exchanges.
Choose your fly line carefully. This line is attached to the fly-fishing rod and may either float on top of the water or sink beneath it. Floating lines are perfect for shallow lakes or rivers, while sinking lines are great for fly fishing with saltwater flies. You may find a compromise between the two with sinking tip lines, which generally float on the water but sink closer to the leader. These work well with wet flies.