What I am going to try to describe is how I used to get horses so light that all I needed to do was 'tighten' the upper calf of my leg and not move my lower leg even 1 inch. If a horse is irritated by a fly landing on his lower rib-cage, I know darn well he can lope of collected and smooth on the exactly where I want him to lope off.
Before I start, I want everyone to know that these methods are for very well started horse -- horses that most people would call 'finished horses'. I am talking horses that know walk, trot, lope off on a correct lead. I am talking about horses that are soft and responsive in the bridle, lope a straight line without a fence and lope a round circle in the correct lead. If a horse is not very well broke -- don't use these methods. They are for 'fine-tuning' a broke horses -- not developing green ones.
First, I find that carrying a crop and raising it is completely unacceptable to me. Threatening a horse with rein ends or crop tells me that the rider has never had a horse that responded to the lightest of aids. Never, never, NEVER threaten a horse.
Nagging at a horse always makes a horse more resistant and less and less obedient. If you are satisfied with begging and nagging a horse 3 or 4 times to get a lope-off in the correct lead, then that is what your horse is always going to require. It also means that the horse will keep requiring more and more pressure get a response.
Getting a horse to respond to the lightest of aids is about ALL mental for the rider. Horses get no more responsive than the worst response that you accept.
Most people just keep upping the pressure until they 'finally' get the correct result. This only teaches a horse to wait for that final amount of heavy pressure and they never learn to respond to the light 'first request'. I have heard many times that "A rider should keep upping the pressure until they reach the point where the horse responds. A rider should use the least amount of pressure that get the wanted result."
You do not have to analyze this very long and you figure out that you are leaving the question of "How much pressure should be applied?" up to the horse to answer. Not going to happen. He is not going to talk himself into becoming 'light'. He is going to get less and less responsive.
I think that making truly 'finished' horses is what high level trainers do and few amateurs (even those that would be considered expert riders and World Class competitors) ever attain. This is why most (not all) World Champion riders have a trainer that keeps them and their horses 'tuned' and ready.
Amateurs and 'trainer wannabes' just keep applying more and more pressure until they finally get the result. THEN, they take off the pressure. If they are going by the rule of taking off pressure for the correct result, then they are teaching the that responding to a very heavy aid is what is wanted. The horse complies -- requiring 5 or 10 times as much pressure as the rider would like the horse to respond to.
[I am sorry this is dragging out so long. I have never tried to put this concept into words before. It is more difficult than I thought it would be.]
Now, the whole things depends on the rider getting the respect from the horse that the horse WANTS to respond to the lightest 'squeeze' or touch.
Say we want the horse to go into a jog with just a light squeeze of both legs. This is accomplished in this way: The rider applies a tiny squeeze. Of course the horse ignores it. Then, the trainer/rider applies about 10 times more pressure than he/she has to but does NOT LET THE HORSE GO FORWARD. The rider can spur the hard 4 or 5 times or 'over and under the horse several times -- hard, without letting the horse go forward at all. Then, gather the horse back up (he is probably a little wound about this time) and ASK AGAIN WITH THE VERY LIGHTEST SQUEEZE. 9 out of 10 horses will now listen to that squeeze. The 10th one may take 'two' overhauls.
Do you see the difference? The first method the rider pushed on the horse harder and harder and the pressure was taken off when the horse finally, begrudgingly responded. That slow, begrudging response is what was rewarded (and trainer for). The second time he was not allowed to respond to the serious overhaul he got and he was ticked to respond to the light aid immediately after that.
The same is true for a lope departure. Ask the horse very lightly with a 'kiss' and a light squeeze with the outside leg behind the girth. If he does not go instantly into a lope, hold him back, spur or thrash his butt and then, quietly reposition him and ask lightly again. I prefer to lope from a walk and not a standstill, but that is just me. I like really smooth, 'head down' departures where the horse pushes off hind end first rather than 'hopping' into a lope with their front ends. It is easier to teach this from a walk than any other way.
Everything you do, should work the same way. You 'over-correct' the horse, bring him back to 'start' and ask again with the lightest possible aid. Then and only then can to get the opportunity to reward the right thing. Do this consistently and you will have a horse that the most seasoned observer will not be able to see you cue.
Again, this is NOT for green horses but only for horses that know what you want and do it consistently but not quickly enough.
A high level trainer that hauls high level youth and amateurs spends much of their time 'tuning up' their youth and amateur horses to keep them light and honest and performing at a high level. Most trainers will tell you that every reining horse, cutting horse or Equitation horse only has so many tune-ups in them. Then, they figure out the difference between the trainer and the horse's regular exhibitor. Most exhibitors then sell that horse to a lower level rider and get a new one that has only been 'trainer ridden'.
This is all because the amateur rider usually accepts less of a response. It is back to old saying:
The worst performance you accept is the very best performance you have any right to expect!!
So, OP -- If you have been accepting a pitiful response, your horse has figured out just how to give you just that.