A golf shot should be a loose, relaxed, whippy motion, much like the rope drill tries to instill. Shawn Clement's perpetual motion drill is another great example of a way to instill this feeling. One should begin the golf swing with a feeling that one is already in motion, not from a static starting position that can easily introduce tension. This is why many players have a swing trigger; it's usually a small movement that mimics the through swing. This is also the reason that some players waggle.
I ran across a good article on a preshot practice routine (may have been Martin Hall) and modified it slightly to meet my needs. Much like a baseball player rehearses at bat, start with the club in the immediate post-impact position, with the toe up and club face facing away from the target line (i.e., wrist watch facing away from the target line) and the club shaft pointing at the target line. Swing back and brush the ground slightly before taking the club to the top (the club should brush towards the right foot). Now swing down and brush the ground slightly, mimicking the club rotation that was the starting point. Keep taking these practice swings until it feels loose and one is brushing the ground consistently back and through. When taking the shot, try to copy the same loose feel.
Practice swings? Take them!! Here's how. Set up as if you're going to hit the shot but so that your club is a foot or so inside the ball (this assumes your lie leaves you sufficient room to do this); this is important because it's the closest approximation to the lie you're facing for the shot and it makes it easier to walk into the shot (careful not to get too close or you risk hitting the ball). Take two practice swings and return to your posture; now "walk the machine" over to the ball and take the exact same swing (this is where you can really become aware of flinching or trying to add to the shot). Your practice swings should incorporate the moves to achieve the ball flight and power you desire. When you're taking your practice swings (relative to the ball position), pay attention to the arc formed by the blur of the club, where the club bottoms out (if an iron where the divot is), or when the club begins rising from the bottom (important for the driver); then make adjustments if necessary (i.e., you're hitting fat or on the wrong side of the arc). Doing this routine will save strokes, because you've effectively taken two "good" swings for the shot; now you're going to move in and recreate a third swing exactly the same with the ball in the way. It can also help you take the flinch out of your swing. This is not perfect but it's definitely a stroke saver.
Most golfers don't put much thought into their practice swings, then wonder why they have no feel for the shot. Instead, focus on making it a true rehearsal of the swing you're about to make: Use the same grip pressure, the same aim, the same tempo. Don't just waste it.
What I believe to be happening with golfers that have a problem reproducing the positive features of their practice swings is that when they step up to the ball (now that there is a result in the balance, and the additional visual demand on the brain of the ball) the majority of the awareness is now taken away from what the golfer is feeling and put into what they are seeing, anticipating or anxious about. To recreate the same thing that happened in the practice swing they would have to continue to pay attention to what they are feeling, as they did in the practice swing.
One logical thing I would suggest in order to make the transition from the practice swing to the swing through the ball is to add a visual component to the practice swings: e.g., focus on brushing a leaf or particular blade of grass, etc., with your practice swings. This shows you if your club brushed the ground in the right spot or not. And if you have the specific problem of swinging too hard through the ball I would offer a temporary, band-aid type fix first: be sure to swing as hard in your practice swings as you are going to swing through the ball (and if you don't like the result of the practice swing don't swing through the ball until you take a practice swing that you like - if the practice swing was bad why would swinging through the ball on the next swing be better?).
You have long term and short term memory. Short term memory is held in the practice swing. If I am playing a golf shot out here the first thing I am going to do is take a practice swing, get a feel for the shot. If I am thinking about my backswing, my forwardswing, my set up, whatever I am doing I am thinking about it right here. After I take the practice swing I am done thinking.
As you take your practice swings, remember to use the same motion, do not think too much, visualize the flight of your golf ball before you address the ball. Having a pre-shot routine and using it before each shot will help you relax. However, if during your practice swings you feel your body start to tense up, step back and start your pre-shot routine all over again.
State your intention with each shot. Tell yourself what you are going to do, then go do it. On your short shots, take the same actions but take a couple practice swings right next to the ball. Rehearse the shot exactly the way you want to hit the ball with the same length swing and tempo. Create the exact feel that you want for the specific shot then simply set up and let your body repeat the feel. Do not give yourself time to think or to become tense over the golf ball. This leads to mishits. Focus on your landing spot and allow your body to repeat the same swing you rehearsed.