A fly rod casts the line, not the fly. The line is heavy enough to load the rod and unfurl forward; the fly is just along for the ride. That's the single biggest mental shift coming from spin or bait.
The motion:
- Start with about 20 feet of line on the water in front of you.
- Lift smoothly to 10 o'clock (your rod tip pointing slightly behind your shoulder). Stop hard. The line lifts off the water and shoots back behind you.
- Pause. This is the hard part. The line needs time to straighten behind you before you cast forward. Count one Mississippi, two if it's a long line.
- Drive forward to 2 o'clock. Stop hard again. The line shoots forward and unrolls. Let the leader land first, then the fly.
- Lower the rod tip as the line settles.
The two killers of new fly casters: starting the forward cast before the back-cast straightens (you'll hear a whip-crack — that's your leader breaking), and bending the wrist at the bottom of the stroke (the line piles up).
Practice on grass before you practice on water. Twenty minutes in a backyard saves an hour of frustration on the river.