To execute a good back set, deception is key. In this video, former Stanford coach John Dunning goes over specific techniques to avoid tipping off the other team to your intended set location.
Dunning discusses some big DON'TS – like thrusting your hips forward, arching your back and looking behind you as you prepare to set. These are dead giveaways to opposing blockers and defenders.
At 1:01, Dunning demonstrates how to "turn the hands over" in a way that helps keep your body position neutral so you can disguise the set.
Also discussed is why the back set has become both more difficult and more important in today's game.
Here is a detailed volleyball training tutorial on back setting from John and former Stanford All American Cassidy Lichtman.