Smog, another thing that will keep your flies out of the bushes behind you is to keep your back cast at a slight up angle, and not let your wrist break too much in the back cast. It is easy to let your wrist go, which wraps your cast around instead of keeping it in a straight line. Back and forth on the cast, not up and around. Here is a link
that explains it better then I do, it is not the best I have seen, but it gets the point accross.
I agree and disagree with the point about nymphing, when you are nymphing, I agree you need to have your fly near the bottom, but I beleive you need to not be "on" the bottom. I think a lot of people mean "ticking the bottom" when they say on the bottom. When I was first starting out, I lost a lot of flies on the bottom, and then was told by a friend who fishes a lot that you should lengthen your leader or add weight to get the fly down so you know you can get to the bottom and you know where the bottom is, then take a few inches off, or a little weight off, to that it is about 6 to 8 inches above the bottom and only occasionally (once or twice in a drift) touch the bottom. You will still snag on the plant growth, and occassionally still get stuck on branches, underwater limbs, etc, but you snag less, and I tend to catch more fish this way.
The belief is that trout don't usually feed on the bottom, they watch the drift, so the nymph needs to be at eye level or slightly above for them to most easily see it.