"Come" is no harder to shape than any other behavior BUT in real life it has a huge component of criteria to raise. Start indoors. Use a clicker and desired treat, not kibble, for several one-or-two minute training sessions daily. Call the dog, and click if he comes toward you. Do this in your living room. Call him from a few feet, and click, when he takes one step, then more steps, of if he comes right to you. Then call him back and forth between two people. Click and treat good responses. Ignore poor responses. If you get more than one or two poor responses, retreat to an earlier shaping step and reshape upwards; this just means you don't have the behavior at that criterion level yet.
Now establish the following criteria, one at a time:
- Come from across the room.
- Come from out of sight.
- Come no matter who calls, to the person called.
- Come fast.
- Come now.
- Come even if you are busy.
- Come (fast, now) even if you are asleep.
- Come (all criteria above) even if you are eating dinner (JACKPOT the first response to this one with a steak bone or really something good).
Now drop all those criteria to zero and establish the same criteria, one at a time, outdoors. If you don't have a fenced area, work in a familiar, bring place and keep the dog on a long line for safety. DON'T correct the dog for mistakes.
Now repeat all the criteria in a distracting and exciting new place. Reduce the distance to two or three feet when you start working around big distractions (other dogs and squirrels are the most famous.) Reinforce a good recall in, say, the park, by clicking and letting the animal go back to the distraction. Very cagey: train the dog to "come" away from squirrels, by using a click, and then permission to chase squirrels as the reinforcer.
Maintaining the behavior
Always utilize natural reinforcers in the dog's daily life to enrich and strengthen the power of your "come" cue; for example, say "come" and when the dog comes, you click and open the car door to go for a ride. Use guests, toys, and other reinforcers for the "come" response. Go to a variable ratio schedule on all levels. Sometimes come gets a pat, sometimes nothing, sometimes a car ride, sometimes dinner, sometimes a meager treat. To keep the responses strong, now and then call the dog away from something enticing, or from a very long distance, even if you don't actually need it to come to you at that moment. You can treat it, or just release it back to its enticement.
Now sporadically ask for and reinforce "come," in highly varying circumstances, for the rest of the dog's life. See? Like many shaping tasks, "come" is simple. But it ain't easy.