After 15 years of teaching golf, one of the biggest complaints I get from my new students is "I can hit it well on the range but not on the course" or "The swing changes I make only last for a few days." If this is you, don't worry you're not the only one.
The reason why this is happening is because of two things: #1 the changes you are making are what I call are superficial changes and #2 Even if you are making the correct changes, you do not know how to mentally implement them in stressful playing conditions." An example could be the typical golfer who changes their grip only to find that it's only helped fo a few days, or the golfer who is able to swing in balance on the range but keeps falling all over the place on the course.
You will know real change when you see the results on the course. These changes come about when you work on the motion of the body as a whole unit, not just a superficial change e.g., in you grip, your left arm position, or right foot etc. If you learn golf or any complicated movement in this way, you end up feeling like you're doing an awkward robot dance! When you want to create lasting changes, you have to start with the motion of the body as a whole. When you learn golf this way, your grip, stance, posture, head position, and overall swing will form itself. Think about it this way: If one were to sculpt a statue the sculptor starts with the general mold of what the finished product is going to look like and then carves out the details later; In designing a car, you build the whole frame and chasis around the specs of the engine not the other way around. Don't be fooled, in golf instruction you will find that there are a lot of myths that are ruining your swing, learning the corrections will be eye opening!! Don't take my word for it, watch how my student's swings all have the classic golf swing look to them, this is not coincidence, they didn't get into that form with complicated motions, in fact many of them were able to get into those positions after the very first lesson. Then from there, making minor adjustments became a lot more natural.
This brings me to address my point #2, how do you take newly built swing and take it on the course? You must take time to practice these new motions on the course, preferably with your coach from time to time to make sure you are not going back to you old habits. It is when you're able to pass the threshold of Stress Induced Muscle-Memory where you will really start to see change on the course. Basically, your body needs to be able to trust your new motions on the golf course and you must mentally feel the postive results. The more you do this, the more you will be able to change your muscle firing patterns. I can't tell you the amount of times I can get a person to swing certain way on the range, but when I take them to the course, it all goes south! Part of Danny Lee Golf Instruction addresses strategies on how to re-wire you brain to accept the changes you've made during your practice sessions.