The different elements of a behavior

It's helpful to think of any behavior as having the following elements:

Distraction in the environment (birds chirping, traffic noise) or in the dog (stress)
Distance (how far away from you can he be and still obey the command? How far can he carry the tennis ball?)
Duration (how many seconds or minutes can he do it?)
Intensity (how hard does he have to push the jingle bells to get them to ring?)
Speed (how quickly does he perform the behavior?)

When we talk about "raising the bar" on a behavior, the truth is that we've got 5 bars, each with their own range of difficulty. So we have to be careful to only raise the criterion of one bar at a time, and when we do, we temporarily relax our requirements for the other ones. Once the new criterion is solidly established, we then work on getting those other elements back where they were. Generally, we want to shape the element of speed last. We want to get the other stuff right before we ask the dog to speed things up.

These concepts apply to all learning situations, by the way, this is not just about dog training. So if you want to improve your golf swing, work on one aspect of it and give yourself a break on the other elements of it while you're learning the new part.

Studying this stuff is fun, it's fascinating, and its immensely applicable in life.