So if you are sitting on a horse that will not move forward off your leg, you may want to touch (not hit) him behind with a whip after you have asked him to go with your leg. You may also want to try having someone stand behind you using voice commands and/or gentle chasing. Remember horses are creatures of habit, so if you use your leg aids properly first every time you ask your horse to go forward, eventually he will respond to just your leg aid without the need for a whip or crop.
If your horse seems totally clueless about moving away from your leg, and you are not familiar with long lining, you can begin teaching your horse to move away from pressure while on the ground. Simply put your hand on your horse's side where your leg will be and apply pressure until he moves over, and then reward him. When you are mounted, try to move the horse sideways a step or two and then go forward. This method works very well for some horses.
The leg aids are also important for communicating to your horse what direction you want to go in. Using this same principle of moving away from pressure, applying the right leg will guide our horse left and vice versa. In higher levels of riding we will tell our horses how tightly to turn and how to position the shoulder, hip and back by the way we use our leg aids. Sometimes we want our horses to move to the left or right while the rest of their body stays straight, such as when a western horse is asked to side pass over a pole in a trail class or when a dressage horse is asked to move across the diagonal of the arena on two tracks (meaning the font and rear set of hoof prints will not follow one behind the other, but the horse will travel sideways so that each will leave its own set of tracks). Riders will use subtle differences in where they use their leg, either at the girth or slightly behind the girth to control the front or hind quarters of the horse.
