Gordy LOVES to heel, probably because he knows it is one of those things in life that he gets handsomely rewarded for!! Plus, he just loves to "play rally" in general, and he knows heeling is just part of the game.
We started with just attention while sitting in the heel position. I lured him to where he was supposed to be, and into a sit. When he looked at me, click, treat! We did this for awhile, just being in the right place, and focusing on me... to me a heel is just as much about the attention as the position. I think getting Gordy's attention was well over half the battle. When he had that first part down I started to take one step with my left foot, and at first it was one step only, looking at me, and moving with me... click, treat! Then I gradually started taking more steps as I knew he could handle it.
When it started to become easier for him is when he started to think that maybe other things, like sniffing the ground, or watching a bug would be better. Our trainer showed us a game where we drop a treat behind us on the ground, the dog will stop to pick it up, and therefore lag. While the dog is getting the treat from the ground, you hold another treat right at your pants seam, and when the dog reaches that heel position, they get a treat. That always keeps Gordy interested, and gets him ready to work and heel.
Another game that helps to get Gordy in the state of mind where he wants to be attentive, and therefore will heel nicely is where I throw a treat to one side of me and tell him to go get it. He runs after it, then I call him back quickly, and as he approaches me I throw a treat in the opposite direction and immediately tell him to go get it... so essentially as he reaches me a treat is thrown, but he doesn't stop running. I call him back and throw one the other way again. I just find that it helps him get tuned in to me.
Any kind of focus games really helped me to get the attention I needed to have Gordy heel.
Now, in class, since we started with one step at a time at home, we had to up the ante a little bit, because he needed to be ready to heel... so in class, I was just a human pez dispenser basically... just treat, treat, treating to keep him in that heel position.
I know from time to time I hear people say that obedience is boring for their dogs, but my Gordy, oddball that he is, thinks it's just the best thing ever ever, so I haven't really had very many problems with boredom with him. Usually if he is bored, it's because he already knows something, and I need to up the challenge a little bit.