If he is young, I would have him on a leash and with a toy or food reward to encouragement him, pat your sides, give the command and walk. He'll be looking at both you and his reward which you have in your hand, so he will naturally fall into place. Walk swiftly with plenty of about turns to keep him focused. Walking in different directions keeps them guessing. Offer praise but don't go overboard to make him excited -- quiet but encouraging 'goooood boy!' will suffice.
As with any puppy training session, keep it SHORT. A few minutes -- literally. Heelwork becomes a major bore if it is overdone.
I have been on walks with Gauge (7 months) with a leash and it's a struggle. So what I actually did today was take him out without a leash on. Played fetch with him for about 5-10 min to wear out the initial energy. Had a treats on my right hand side pocket and a clicker in my left hand. Note: Gauge knows what a clicker means and keeps steady eye contact with me in his "sit" position before I release him to eat. Probably two things your dog should learn before attempting the next part.
Started off at first clicking and giving a treat for being in the correct heel position. If he would run off, I would run the opposite direction making sure he heard my feet but not saying a word, then he would run back to me. He'd line up in the correct heel position again...and I would click again...constantly clicking and giving a treat while in this position. Then we worked on eye contact. As soon as his eyes and my eyes met, click and treat, all this while walking in this heel position...yes you have to keep looking at your dog.
Baby steps for now...but he was doing excellent today. Highly recommended training method if your dog is food motivated.
Yes, we've been going to puppy class for three weeks now but they haven't addressed heel. She knows to sit, down, shake, and wait (until I release her to eat or cross a street). She's a very quick learner so I think with all of your suggestions and what I've read up on, we'll get it in no time! Her biggest challenge is ignoring other people walking down the street and other dogs. She just gets SO excited! I'm not sure why I didn't start working on heel with her first, but we are starting now!
Do you want a formal heel (dog glued to your left side, sitting when you stop, turning with you) or do you want a less structured loose leash walk? For every day strolls etc I'd recommend a relaxed loose leash walk - my rule is that the dog has the length of the leash to roam around, but pulling it tight means the walk stops instantly.