The 'HEEL' position is behind the line of your left thigh. Walking in the HEEL  position is taught separately to sitting at HEEL.

LURING your dog to walk at HEEL is a very easy exercise.  

I always begin to teach my chocolate labradors this luring exercise beside a wall, preferably inside the house where there are no distractions. The wall ensures that the dog stays square to your position. Your dog is between you and the wall. And this will also ensure that your dog learns to stay close to you.

I commence all new training routines 'indoors' before venturing outside and to a park. The dog needs to learn a routine without exposure to distractions. You can progressively introduce distractions.

CARRY A TREAT POUCH. You'll need a lot of treats. 

Remember that the 'heel' position is behind the line of your left thigh.

Place a piece of food in your left hand between your index finger & thumb. Position your left hand adjacent to your left thigh with your palm open and aligned to the rear. 

Hold the treat under your thumb. 

Your dog will ‘target’ the food in your hand and automatically position its nose in the palm of your hand. 

Give the command, ‘Heel’, then commence walking and ‘lure’ your dog. The food is the ‘target of the lure’.

Walk 3 paces, then ‘mark / confirm’ the behaviour by saying 'YES'. Then,... promptly release the food, not before 1 second.

'YES' marks & confirms the successful behaviour and the dog begins to anticipate the treat. This is the essence of ‘Reward Based Marker Training’.

'YES MEANS TREAT'

Repeat this exercise, like all training routines, a minimum of 20 times each session. Progressively increase the number of steps you take. If the dog loses concentration, reduce the steps / shorten the distance / reduce the time duration.

If your dog gets ahead of you, reverse your direction 180 degrees and repeat the lure.

As your dog advances, you can vary the routine by turning left, right, side step, figure eight, saying 'heel' at every turn. 

The sit position will quickly become automatic when you stop. Soon, you will not need to give the sit command.