Successfully catching a lot fish on the rise requires very accurate casts. Aside from the principles of casting accurately (solid footing, all the line out you need before you cast, holding the rod like a hammer no or few false casts, upright rod action, same line length out, the right leader length, watching the spot you want the flies to land in and casting very quickly to a rise) the next most important thing is positioning.
The key part of positioning is getting yourself into a position where there is only one variable that you are dealing with. If you are side on or directly behind a fish you have a much easier cast than if you are on an angle. On an angle you are dealing with both distance ahead and to the side of a fish. It is far easier to cast accurately when you only have to deal with one variable.
Good set up for a cast.
Where possible fish from directly behind or at right angles to the fish. This makes casting accurately a lot easier.
Poor set up position, far harder to hit the target area because there are two variables that can go wrong.
Picking the fish to cast to is another key part to successfully catching fish. Always try to find a fish that is rising regularly not sporadically so you can find your range and make multiple accurate casts. It is unusual to catch a fish that only rises sporadically as it is hard to be accurate.
In my local rivers the small fish seem to rise more regularly but demand a more accurate cast. It is easy to pick the size of the fish from the rise forms, with little fish making a splashy rise while big fish make a bigger slower rise forms, and you can often see their neb and forehead.
The fish above 3lb will not rise as freely, often only rising four or five times before stopping, but they will be much more willing to move to take a fly. If you see a big fish move aggressively too it and get your flies to it quickly as it will be off quickly, but will be more likely to take a cast that is not perfect. Smaller fish allow a bit more time, but make the cast perfect or you will not get the take.
When fishing the mayfly hatch do not be tempted to fish to fish that are down stream of you. Despite many years of trying this is not something I have ever been consistently successful with, so I always try to find a fish directly across the stream or upstream of me.
Wading through a pool is a huge sin if there is a long wade between fish. Your bow waves will put fish behind you down, and it is almost always a lot quicker to get out of the water and walk up or down the pool then get in again when you are parallel to the fish.
I. Fishing the Evening Rise | II. Flies | III. Strategy | IV. Strategy II | V. The Take & Playing the Fish | VI. A Parachute that Floats | VII Smith Creek Rig Keeper | VIII. Tying on Flies in Low Light