Here are links to two posts in another thread with videos: post 1 post 2
posburyfan, what you describe isn't exactly what I know as choose to heel. What I've done is start with my dog generally near me, toss a treat behind me, and start walking. Most dogs will try to catch up. As soon as the dog is in heel position: click, stop, reinforce. Repeat several times, then take a break. As all of our instructors have said, heeling is hard mental work for the dog, so we don't do it for long periods.
As soon as the dog is reliably walking in heel position, you can start reinforcing as you walk. Start with quick reinforcement (every 2-3 steps), then slowly start increasing time/distance. Verbal cues aren't added until the behavior is very, very solid.
I'll just note that my older dog and I have take two 6-week classes that focus entirely on heeling and we're not even close to competition level. If you're looking just for loose leash walking (LLW), that's different and much easier to train. There's a sticky for that: "Loose Leash" walking