Let's say your fishing a nice run of water where you know there are at least half a dozen nice trout spaced out along the length of the run. Well, you quietly enter into the water & wade to a spot where you can get your line to drift where the trout are probably at. There are two things you want to keep track of as you fish this run & they are the length of line you have out & where your feet are.
First, find something to aim for like a tree branch or a root protruding from the water. It's much easier to cast to an object like this than it is to hit an open space of water. With each cast, keep letting out more line until your casts are reaching just in front of your target. Once you get the distance figured out, take note of how much line you have extended from the end of the rod. In order to be consistent & reach the same location every time you cast, you'll need to know how much line you have out. As you begin to catch some fish, you can adjust this length of line to hit different parts of the run, especially as the trout move in the drift. I know of some anglers who actually mark their fly line at different lengths with a ink marker. This way, they know when they've let out 20 or 30 feet of line, etc.
The other thing to consider in this situation is where your feet are. If you're fishing a run, you've figured out where the trout are almost exactly, & you know the amount of line you have out, make note of where your feet are. By doing this you'll know that your casts are hitting the same exact spot every time. You can put all of these things together to get really good accuracy consistency from cast to cast as you work your way down through the run. After you quite getting any action in one spot, simply move a few feet down stream. You'll have the length of line & you feet to use as a reference to find the trout.
These techniques work especially well when you're fishing to trout that aren't rising & also when fishing a seam in the water. A "seam" is the part where slower water & faster water meet, usually resulting in a "slick" section of water. Wherever you see a seam in the water, fish it. Trout love to hang out under these, because they provide food & are next to some kind of underwater cover - which slows the water down & creates one half of the seam.