In The Beginner's Guide to Dog Agility: Fun, Frolic, and Fitness for You and Your Dog! Laurie Leach gives a summary of the body language used to communicate information in agility:
Eyes - Your dog is aware of where you are looking, look at the obstacle you want him to perform next.
Shoulders - They are a powerful communication tool. A turn of the shoulders indicates a change of direction, and the degree of rotation tells how sharp the turn will be. A drop of one shoulder is a cue that the handler is going to rear cross, or cross behind the dog.
Arms - There are three basic ways to use your arms, all arm signals are given with the arm closest to the dog. Bowling the dog is where, palm up, you swing the arm towards the next obstacle. Drawing a path is where you point with one finger moving your arm to show the dog the correct path to the next obstacle, so your arm is close to your body if your dog is to stay close to you, and your arm is outstretched if your dog is to stay further away. Pushing is using an open palm and a push motion to widen the dog's path away from you.
Feet - Dogs, particularly small dogs, learn to read your feet like the arrow on a compass. Your feet should face the next obstacle as soon as possible.
Position - Your position in relation to the dog also tells it where it is to go on course. Lead outs and front and rear crosses give precise information about where the dog is to go next.