When asking a horse to move forward, first you should squeeze with your legs, then use your spurs (if you are wearing them), and finally go to the crop if the horse still doesn’t respond. This is always the sequence of aids in driving the horse forward; consequently, the animal learns that if it doesn’t respond to your leg aid, then your punishment will escalate from leg, to spur, to crop.
If the animal doesn’t respond by moving forward willingly and alertly, then you need to use the crop more forcefully until you get the horse’s attention. It is not good to simply pester a horse by tapping it incessantly with the crop, for then the animal will rely upon it for almost every forward step and will never really carry you on a pleasant ride. Also, the horse will become a sour partner that may get fed up with being tapped all the time and begin to balk, back up, or rear.
Remember to only use enough force with the crop to get the response you want—no more, no less. If you are methodical about your leg, spur, stick sequence, you’ll find that your horse will begin to respond much better from leg pressure in anticipation of the other, stronger aids.