Spooking the fish should always be a top concern to any angler. After all, it doesn't make much sense to scare what you're trying to catch! Whether it's totally flubbing a presentation, slamming boat hatches, or projecting a long shadow on the water, there are plenty of ways to scare the crap out of your finned quarry and send them fleeing. Relating to the last one, I'll use (almost) any means necessary to lessen my chances of being spotted. Sometimes on open, flat, barren banks there aren't a ton of options, but often you can use the lay of the land and your immediate surroundings to help conceal yourself. Here's a few ways I use features around me to switch into ninja mode.
Natural and Man-made Features: While tall foliage, big boulders, and certain unnatural structures can hamper both access and casting, don't let that stuff frustrate you too badly—use them to your advantage! Hiding behind or within various shoreline features is a great way to stay out of sight from wary fish. I've caught plenty of overfished, paranoid trout in small streams while crouching behind large streamside boulders or bushes and peeking over the top or around the side just enough to fish effectively. It often was a bit uncomfortable and didn't put me in the easiest casting position, but sometimes it was the only way to not immediately blow out a spot. Even if you can't fully conceal most of your profile, just making your presentations while not totally standing out in the open can give you that necessary edge. If available, wearing naturally-colored clothing that helps you to blend in even more effectively never hurts.
Shadows: Fish love to hide in shadows since they get protection from sunlight and concealment from predators above and below the surface. As anglers, we too can use them to our advantage. Not only will your profile be less obvious when standing or (better yet) crouching in the shadow of a tree, bush, building, or whatever, but standing in a good solid shadow also means you won't cast any fish-scaring shadow of your own—often times a very good thing. And hey, on a hot day who doesn't like some shade anyway?
Depressions: Sometimes, a shoreline will have a lip or low spot. Standing on this lower ground is a great way to reduce your profile without having to uncomfortably kneel or crouch down quite so far or even at all. The picture at the beginning of this post shows me using both the shade of a tree and a modest shoreline depression while stalking a group of very skittish grass carp in Arizona. Unfortunately my efforts didn't result in any hookups, but I was able to get much closer to those fish than I ever imagined, all without having to kneel or crawl around on the ground. I had to stand back from the shoreline a ways to stay in the gut of the depression, but by crouching only slightly I stayed low enough to not be threatening yet still had a decent line of sight and comfortable casting angle to sight fish effectively.
I always imagine what a fish might be seeing from its point of view and how I can use cover and angles to best stay concealed. Often times, doing so requires a little extra thought and effort, but it can really work in your favor. Just remember that in situations where the fish have a decent chance of spotting you, your odds of success go up the more you can blend in and the lower of a profile you can maintain. Keep these simple tips in mind....I hope they help you become a more successful fly angler!