Over all the years of my guiding there have been a few constants in the success of catching fish, one of those is that spooking fish is a horrible finish after all the hard work of finding them in the first place. I am sure that I still have things to learn on how not to have this happen but right now I have a pretty good grasp on what to and what not to do on this topic.
Sight is usually the key to staying out of trouble. If you can see fish far enough out then you are ahead of the game, after all not running them over with the boat is always helpful. Sometimes the fish dictate this in a nective way, they sit a little deeper, pick a muddy area to reside in, and/or hardly move. Other times fish will have their backs out of the water with birds over them chasing the shrimp they are kicking up. Most fish are somewhere in the middle, with a momentary flash of white from their underside or water that is just slightly shaky. Being vigilant equals seeing fish and if you see them early you can be prepared.
While you are poling to where they are there are things to do to make sure you don't make the fish aware of your presents. Don't think you need to get there in the next few seconds, pushing the boat extremely fast is more likely to create pressure waves. Keep someone on front so that the bow stays down and doesn't slap, be tender with the pole when you first make contact with the bottom to avoid crunching noises, no one in the boat should be picking up their feet unless they somehow can keep those feet from returning to the boat surface, as the caster don't sway because rocking the boat will make pressure waves, and minimize talking but when you do talk make sure you do so in the direction of the other person so you don't have to talk as loud. As you approach make sure you are 100% ready to cast, you should always be, but if you have this luxury then you have no excuse. When poling the boat you need to make sure the boat is positioned properly, if possible, to put the fish in line with the casters strongest ability as far as his cast.
When you get to the casting range don't cast in the middle or to the other side of the school. The fish on the other side are just as fishy as the fish on your side and if you pull one off your side then most likely the others will not spook as bad as if you lay fly line across the school and or pull a fish through the school. Know your depth so you know the heaviest your fly has to be to get to the bottom, in other words if a light fly will do the job then it will do it better.