Heel is a very specific position where the dog’s front feet should not go past your back heel.
Step 1: Start With The Dog Facing You
Use treats to reward the dog whenever they are in the right position. Start with the dog facing you.
Step 2: Lure Into Position Behind You
Show the dog a treat and in your left hand and then moving your arm in an arc lure the dog into the correct position behind you. The longer your dog is the wider the arc has to be. The dog has to be encouraged to sit behind you. If you do it too narrowly the dog will sit sideways to you.
Step 3: Reward Your Dog When It Gets Into The Correct Position
Reward your dog when it gets into the correct position. Then turn and face your dog and start again.
Step 4: A Half Step Back Will Encourage The Dog To Move Behind You
Some dogs will hesitate to move behind you. If so, you can take a half step back to encourage them to move into the right position. If your dog is moving behind you tentatively don't expect it to move to the sit position immediately. When it moves behind you readily, then you can add the sit.
Step 5: Add Some Movement
Once your dog is following the lure and finishing in a sitting position behind you, you are ready to start adding some movement. Start small - just take one step and reward your dog if it stays behind you. Keep your left hand with the reward in it, behind your left leg. This will encourage your dog to stay in position.
Step 6: Gradually Add More Steps
As your dog gets used to being in the correct position gradually increase the number of steps taken at a time,
Step 7: Keep Your Left Hand Behind You
Keep your left hand, with the treat inside, behind you.
Step 8: Use A Leash When You Introduce A Distraction
If your dog is easily distracted or if you are working outside you should use a six foot training leash. When you are working inside you can also introduce a distraction such as your dog's favorite toy. Remember, use the treat to train the dog to heel - not the leash.
Step 9: Gradually Increase The Interval Between Treats
As time goes by you should reward your dog less and less frequently. You should work towards giving a reward every five or ten seconds.
Step 10: When The Dog's Attention Wanders Give A Treat And Use The Heel Command
If your dog attentions wanders give it the heel command and reward it when it returns to the correct position,
Step 11: Only Reward Your Dog When It Is In The Correct Position
Pay attention to your timing. Only reward your dog when it is in the correct position. It you are having trouble keeping your dog in the right position check your hand position. Make sure your hand is behind your left leg when delivering treats.
Step 12: Next - Only Reward Your dog On The Free Command
At this stage you should introduce the free command. Stop walking, move your hand around to the front and give the reward after saying the word "free".
Step 13: Change Pace And Introduce Turns
As your dog's proficiency increases you want to start introducing changes such as turns, changing pace or stepping to the side. The aim is to get your dog to walk at heel in all different situations. If it gets out of position give the heel command and reward it when it gets back in position.
To see this training in action check out this video from K9-1.