Mark Rippetoe has a new article up over on T-Nation:
Proper Back Position for Power
This article is an excellent example of coaching cues.
Fix one thing at a time - He's got a specific aim in his cues - to get trainees to initiate a proper lower back arch in order to maximize their ability to lift safely and powerfully.
Have different cues for different people - Not everyone learns the same way. He's got cues for visual people, for physical cues people, for people that respond best to exaggerated vulgarity. Not just one cue, but a number of them, in a progression, he can use until everyone is doing it correctly.
Reinforce the cue immediately - After cuing the proper motion, he has the trainee do the exercise that needs the fix - be it a squat, deadlift, or press. This is done while the trainee still feels the effects of the isolated movement that was cued, so the trainee knows how it should feel under the actual weight.