Part II: How to Approach Small Streams:
Observe, Position, and Improvise
The challenging thing about small streams is that they are often plagued with more 
hazards than a Scottish golf course. Of course this is a good thing because the same hazards make for great trout habitat, providing cover and safety from predators, well-oxygenated riffles and a constant supply of passing insects. But deadfalls, sweepers, cutbanks, rootballs, and overhanging bushes are all potential fly hazards that come in a myriad of combinations. Even the smallest twig cutting the surface disrupts the current and will send your fly reeling off in unanticipated directions or will pluck the fly from the surface and refuse to let go.
Snags and the odd break off are unavoidable; however there are precautions you can take to minimize the inevitable. When approaching a stream observe and identify potential hazards. Look through polarized glasses and study subsurface structure and possible snags. Then study the movement of the current- its slack water and eddies, seams, and riffles. If a trout is feeding on a seam or holding under cover, it’s imperative to float or drift the fly over the trout. Decide the best position and angle to accomplish a cast into the feeding zone and move slowly and quietly. In most cases it will be directly across or slightly upstream where you can settle the fly and have it float or drift naturally into the zone. However, often branches or deadfall prevent this avenue so casting from a downstream position may be the only alternative.
Guerrilla Casting:
Once you have observed the surroundings and decided on positioning, you now have to decide how to best get your fly into that limited feeding zone. Dapping and flipping in really tight streams is often all that’s required. Use the roll or steeple cast to avoid trees behind you, however, overhanging branches on the far side of the stream will complicate even these casts. For slightly larger streams, there are many different approaches including sidearm casts, underhand casts, and skip casts which take some practice but will improve your arsenal for getting in, under, and out of hazardous spots. Creativity and improvisation is your best ally when you are in some really ugly spots and have to resort to guerrilla casting.
In extreme brush-intensive situations, I occasionally use the sling shot approach. I estimate the length of leader needed to reach the holding water then grab the fly end of the leader with my line hand and hold the rod parallel and low to the stream and pointed directly at the spot I want the fly to land. I pull on the leader creating a back bend on my rod. I then angle the bend according to how low I need to be to avoid the overhanging brush and let fly. With a little practice you’ll be able to do it without having the fly stick in your hand every time. 
Mending Time:
It is also imperative to mend line to maintain a natural drift. On small streams mending is often not as crucial as the length of line on the water is considerably less than on larger streams. Learning how to stack line or stack-mend is also a useful skill. It enables the fly to remain in the zone of an eddy or flat water instead of being dragged downstream by the rushing current. Stacking line is also a good way to allow a streamer or heavy pattern to sink before high-sticking.
The best way to learn is to have someone actually show you – but the basic idea is to pile extra line near your fly so the current takes the excess downstream and leaves the fly floating in the sweet spot for a few seconds longer. To accomplish this, strip out an extra length of line and loop it in your line-hand. When the fly lands, take your rod tip back slightly and perform a series of abbreviated roll casts while feeding the extra line. The line should roll up and stack over the leader/line without moving the fly – of course, like anything, it takes practice – lots of it- I mean I should probably go practice right now...