In fly-casting it is the weight of the fly line that carry's an almost weightless fly to the target; you have to learn to use the fly rod's action to cast the weight of the line.
Keep slack line out of the system. The line should always be straight before the power of the cast is applied, only a straight line can load (store energy) in a rod, slack line wastes some of your casting stroke. It is the weight of the fly line, which causes the rod to bend and load or store energy, try to eliminate all slack line while casting.
A) Correct starting position as soon as we move the rod tip the straight line will begin to load the rod.
B) Incorrect starting position this position of the rod causes a belly of slack line; the first part of the casting stroke is wasted straightening the slack line. Only a straight line can bend and load the rod.
Concentrate on keeping hand, wrist, forearm and shoulder in a straight-line. The tip of the rod should trace a straight horizontal path while casting. A straight horizontal path of the rod tip during the casting stroke concentrates all the energy of the cast towards the target. The tip of the rod should travel in a direct path towards or away from the target. Along a horizontal path the rod will work to its optimum. Concentrate on a straight-line flow of energy. Loop control is achieved by the ability to control the rod tip during the casting stroke.
A) Horizontal path of the rod tip.
If we trace a straight horizontal line with the rod tip through out the casting stroke a Perfect loop will be produced, one where the top portion of the line and the bottom portion of the line are parallel to each other. Along this horizontal path the rod works to its full potential. Good fly casters have the ability to cast their loops close to a perfect horizontal plane.
B) A convex path of the rod tip.
Wide open loops are formed when the back cast and front cast is separated by more than 180 degrees, this is caused by using a wide casting arc, usually caused by breaking the wrist on the back cast or by not applying force to the rod, leaving the rod in an unbent (unloaded) state during the casting stroke causing the rod tip and line to travel in a half round convex path. We must force the rod into a bend and then force it back out again with a positive stop. An open loop, one where the top and bottom portions of the loop are widely separated, disperses energy in to many directions, the energy is not concentrated towards the target and the line goes nowhere.
C) A concave path of the rod tip.
Tailing loops are formed when the back cast and front cast is separated by less than 180 degrees, they are caused by using a casting arc which is too small for the amount of bend (LOAD) in the rod or by applying to much force at the beginning of the casting stroke. Match the amount of rod bend in the rod to the casting stroke and progressively increase the velocity during the casting stroke, finishing with a crisp positive stop.
Remember - All tailing loops are caused by a concave path of the rod tip.
It is absolutely imperative that we finish both front and back casts with a positive stop, it's not always in the same position because of the varying line lengths we use, but it should always be there. A Crisp positive stop combined with a progressive application of power is the key to good fly-casting.
To keep the rod tip tracing a horizontal line path we need to match the amount of bend (load) in the rod to the casting stroke, the deeper the flex in the rod or longer the length of line the longer the casting stroke must be.
A) Short length of line, short stroke.
B) Long length of line, long stroke.
A fly rod is a flexible lever it bend's and loads during the casting stroke, the more force we apply the greater the rod bend's or loads, it is important to remember that a fly rod is not rigid, it is possible to cast tight loops with both short and long casting arcs if we match the casting stroke to the amount of bend in the rod.
We need a smooth and progressive application of power and velocity finishing with a crisp positive (STOP) at the end of the casting stroke. This abrupt STOP releases energy from the loaded or flexed rod into the line and forms the loop. A smooth Progressive application of power and finishing with a crisp positive stop.
Wait for the line to fully straighten before you begin the forward or back cast. We need a long pause for a long cast and a short pause for a short cast. Keep your shoulders square to the target, watch your back cast from time to time to see if the line is fully extended before making the front cast, make sure you just turn your head not the whole body as this will swing the cast behind you. You can also judge your timing by watching your front cast unroll and waiting for the same amount of time on your back cast. This visual help ensures perfect timing. Remember we can only make a good front cast if we make a good back cast. Work on the back cast; concentrate on a positive stop, a tight an efficient loop on the back cast sets us up for the perfect front cast.
I cannot emphasise this enough, don't wait until you are on the water to practice casting, It is impossible to practice casting while fishing, there are just too many other things to concentrate on. Practice on a lawn or a pool free from obstacles and distractions, every hour spent practicing will bring you closer towards fly casting efficiency on the stream. These tips have been put together after years of fly-casting and fly-casting instruction. Let me stress that these tips are not the bottom line; there are more ways to teach fly-casting than there are fly fishermen. Just use what works for you to make your casting more efficient.