Tips and tricks.

Tackle.

Florescent Beads:You can buy Fluorescent beads from any tackle shop that make excellent bite indicators. I think they are intended for the sea angler as an attractor, but they float well and make fewer disturbances than putty. In addition they never fly off, I pass my leader loop through them, then attach my leader to the line loop.

Fullers Earth: This is powder that you buy from the chemist for a couple of quid, mix it to a paste using a non-perfumed washing up liquid. This makes an excellent line sinker better than gink! I usually fill up an empty film holder with it and put it generously on my small spiders.

Petroleum Jelly: The loop end of your floating line takes some bashing, so to keep it floating I treat the first 2 feet. It floats easier and makes bite indication easier. Often a sinking Floating tip spoils the presentation of Dry Flies so this is a good emergency tactic.

Inch marks: If you paint dots on you rod just above the handle in intervals of an inch, you can measure your fish while you have your hands full.

Gold Heads: I always carry a few gold heads, so I can sink flies to the bottom. You can tie all you nymphs and wet flies without weight. When you need to sink them just simply thread the gold head on the leader and tie on the fly.

Mud: Fish have a sense of taste and smell that is supposed to be hundreds of times better than a human. To take off the smell of perfume and soap rub your hands in some bank side mud for camouflage. Rub your nymph and wet fly as well.

Technique.

Use of Cover: What most people associate in "stalking" is staying off the horizon and using the cover of trees. Well here's a common problem, what if you're in the middle of a stream wading. Approaching from a down stream position gives you the element of surprise. To increase your advantage, position yourself behind major boulders.

Short Lines: The first thing you need to do when fishing a river (especially a small one) is to cast out not more than three-rod lengths. This will seem alien to lake fly fishers!
But basically the presentation is better, the control is better, and as you are not scaring the fish you are catching them!

So There!

Move Slow and avoid wading: The slower you move and in small steps, the less again you will scare fish. Do everything slow, don't make sudden movements. If it takes you a few minutes to change a fly tough, the fish will be still there "unspooked.

The induced take: Frank Sawyer the master fisherman knew what he was talking about when it came to wet fly & nymphing. He developed this technique. Cast an about 2 feet to the side or upstream of you quarry.
Keep a straight line between rod tip and leader (lifting the rod as fly approaches).
When you think the fly is within nibbling distance gently raise the rod tip making the fly rise as if it was hatching or escaping.
If you do it right the trout sees the fly approaching and plays it cool, it waits to the last second for its lunch.
As the fly is pulled away I thinks its cover is blow and makes a quick dart to get an easy snack.

The Vertical Plop!: If a fish is really close or near a tree cast the line at about 75 degrees and pull the line back so the fly simply drops out of the air. This works great with Gold Heads; the fly should hit the water first. Again you can perform an induced technique as well. A great one if you fishing to a far bank and a rise occurs at your feet.

The Line Shoot: Here is a technique that I re-cycled from lake fishing! You can accelerate your line through you rod by "pulling or hauling" the line towards you, at the point before the punch of the cast.
On a lake this is commonly used to increase distance in your casting, in their river scenario this is not the problem but bank side vegetation is.
I commonly use a side cast as the trees are often behind, above and to the side of me. I often cast with a narrow arc maybe as little as 30 degrees, casting is only possible as I "Haul" the line as I cast. This means unfishable areas are now available.
In addition if I am stalking a particular fish and I mess up a cast I can recover it by hauling while in mid air. This is a very important technique, so it is well worth investigating.