1. Match the hatch
Open your eyes and observe what's going on around the water when you reach the bank. Whether you're on a river or a stillwater, it's probable that the insect life you can see on and around the water will be just what the trout are feeding upon. Try to match the hatch and pick a fly that is the closest match to the insects around you.
2. Watch the rise patterns of the trout
If there is little or no sign of a hatch but you can still see fish rising, their rise patterns can give away clues about the flies they're feeding upon. The rise pattern, or rise form, is the splash the fish makes as it reaches the surface. Big, splashy rises are often a sign that the fish are coming up quickly from deeper water to smash flies on the top, while less splashy rises, where you see the dorsal fin and tail break the surface are typically a sign of fish feeding upon emergers just below the surface.
3. Use the right tippet material
Using the wrong tippet or leader material can give you poor presentation when fishing dry flies. If your tippet is too thick, too stiff or too buoyant, it will lay on the surface tension and be highly visible to the fish and they're likely to ignore your fly. Most dry fly experts now favour fluorocarbon tippet material as it's thinner and denser than copolymer or monofilament, so it drops below the surface tension where it can't be seen. Fluoro also has a lower refractive index, which means it's much harder for fish to see below water too.
4. Scale down your tippet diameter
Scaling down the diameter of your tippet or leader material will give you better presentation and makes it harder for fish to see your fly. Thinner tippet is generally also softer and this makes flies look more natural to fish too. Combined with the less visible appearance, it should get you fewer refusals and more takes. If you find that fish are refusing your fly, try changing to a thinner, softer tippet material. A thin fluorocarbon or some Stroft GTM is well worth a try.
5. Use a smaller fly when fish are fussy
When fishing dry flies, a lot of novices often choose a big, bushy pattern because they struggle to see the smaller dry fly patterns. However, while this sometimes works, when fish are fussy or locked-on to a specific type, colour or size of fly which is common in the area, scaling down to a smaller fly is a better idea. We quite often fish dry flies down to about size 20 when conditions are tricky and the fish are fussy. You'd be surprised at the size of the fish that take them and the strength of such tiny hooks!
6. Take the shine off your leader
If you're fishing a copolymer or monofilament line, or a cheaper fluorocarbon which is sitting upon the water surface, it will really impact your catch rate. Even though it's very thin, the line will be extremely visible to the trout beneath and they'll probably refuse your fly as a result. It's sensible to de-grease your leader by applying some Fuller's earth, like Fulling Mill's Fuller's Mud, to your line every so often. It helps removes oils from the line and roughens the surface to take off the shine and make it sink a bit. It makes a massive difference when fishing dries.
7. Treat your fly line to help lifting off
Over time, your fly line will build up a layer of dirt or grime and it can lose its buoyancy. Rather than sitting high upon the water surface, it will sit within the surface tension and will splash as you lift off. Cleaning your fly line and applying a fly line treatment or line dressing, especially one based on silicone, will help it float higher on the water lift off with less splashing. Mucilin or Barrio Fly Line Care are well worth a try and can also be used when on the water.
8. Don't leave your flies in the same spot too long
One thing that you'll notice if you watch any of the best competition fly fishers is that when fishing dries they rarely leave them still for long. Most of them cast their dry fly to their chosen spot, perhaps covering a fish that has risen nearby recently, and then count to five. If nothing has gone for the fly within five or ten seconds, they'll re-cast somewhere else and try again. Having been using the same technique myself for a couple of years, I have to say it's definitely much better than leaving your fly in the same spot for longer.
9. Don't strike too quickly
This one is harder to do than it sounds, but you need to resist the natural urge to strike as soon as the fly is taken. Fly fishing experts from the last century used to encourage their pupils to say "God save the Queen" before striking. Wait a split second and then lift and you'll generally find the fish attached. This is particularly wise when the trout are fish are doing those splashy rises next to the fly to sink it before turning to take it beneath the surface.
10. Dry out your fly between casts
Obviously, you want your dry fly to be floating upon the surface (unless you're fishing an emerger or a pattern like the Shipman's buzzer, which is designed to sit within the surface tension). There are many ways to dry out your fly, from a couple of quick false casts between casts, to the use of an amadou patch, a rubber band to ping off the water, or the use of desiccant or floatant.
11. Use the right floatant for your fly
Not all floatants work on all types of dry fly. Liquid silicone gel floatants, such as Gherke's Gink or Fulling Mill Dry Sauce, are great for hackled patterns if you warm up the gel first and then gently rub it into the fibres. But they will clog fly patterns made with finer materials, such as CDC feathers, which will cause them to be less buoyant. For CDC patterns, you ought to try a CDC oil, or my preference, use a hydrophobic fumed silica powder like Frog's Fanny or Fulling Mill High Glide.
12. Use a fly line with good presentation
You can't just use any old fly line when fishing dry flies. Certain fly line profiles, especially those designed for distance casting, are often quite thick and heavy at the head end and don't always land that delicately. More subtle fly lines with a presentation style taper are a much better choice and land more softly. The Barrio Mallard or Barrio GT90 both work really well for fishing dries.
13. Lift back at the end of your cast
There are a few ways you can help your leader turnover at the end of your cast and ensure your flies land a bit more gently. Personally, I prefer to stop high and gently lift back at the end of the cast. This gently pings the line back a touch which not only turns over the leader, but also sees the flies float quietly down without a splash, much more like real flies would.
14. Use a lighter rod
You'll get far better presentation if you scale down your line so it's lighter. While you can fish dries on an #8 line, your presentation isn't going to be very subtle. A lighter line, like a #5 or even a #4 , can make a big difference to the delicacy of your presentation. As such rods are generally a bit softer too, you'll also bump-off fewer fish.