Ian Heaps on Fishing

is an excellent (out of print) book by Ian Heaps (isbn 0-907675-02-6). As usual I'm going to quote from a few pages:
The best way to improve is to practice.
You must feed according to how many fish there are and how they are feeding.
There was a method though, and that was slowing the bait down… the caster needing fishing in a very different way to the maggot.
You must keep it as simple as possible: fish as efficiently as you can.
You must learn to feed on a regular basis so that the fish are charged up, and they get to know exactly when the next amount of food, is going to arrive.
Especially on a river which is flowing, the most important thing is to get a feeding pattern going. Then, there are a thousand and one shooting patterns which will catch them.
If you see the float lifting up a bit when it should be bullying its way through the swim, it is not big enough to do the job.
For me, far too many people are obsessed nowadays with fishing light. All too often they do not experiment and put on enough lead.
Generally speaking, I have found that the more lead you can get on the line and still present the bait properly the more, and the bigger, fish you will catch.
Practice makes perfect, and there is no substitute for experimenting yourself.
If you put on a number of smaller shot and bunch them together, you can soon space them out if the feeding pattern changes.
John [Dean] did the same thing as everyone else - only he did everything just a little bit better.