Be careful what you wear, colors that blend with the surrounding or that are muted enough that they don't make you stand out against the background behind you. It is also good to walk softly and as much as is possible to avoid wading. If you must wade, do so extremely slowly which not only lessens noise, also can help lessen falls.
There is a great little book called, "Curtis Creek Manifesto" that is a great instructional tool. You also might want to hire a guide for a half day or a day. They can help you hone your skills and even teach you a few things that might lessen your frustration tremendously.
Last but not least as others have said, the less you false cast, the better. I have found in the park that it is more a case of "chuck and duck" than casting. Be sure as well to be careful to "pick up" your line as you begin to retrieve or before beginning your back cast. Do this by lifting the rod tip so as to lift as much line as possible off the water, which lessens the amount of disturbance of the water by the line.
"Fly-fishing has many attributes, but none more pleasing than it's ability to liberate the young boy that still hides within me and to let that boy live again without embarrassment or regret, sorrow or anguish." Harry Middleton