I always play a soothing music in class for Shavasana. It's a piece of music Azmi used to play during Shavasana in his class. I love it because it calms me and I can relax myself by listening to it.
There was once I'm not sure whether it was the CD or the player, the CD got "stuck" and couldn't play. So I tried to relax the class verbally with "release any tension at your joints", "do not hold any part of your muscles", "listen to the rhythm of your breathe" kind of words. Lastly I reminded them "but, do not fall asleep". Someone raised and looked at me "Do not fall alseep?"
All of us love Shavasana, but it's not easy to lie down on the mat comfortably with eyes closed but do not fall asleep (especially after a workout). I've noticed people dozed off during Shavasana, and I used to have wandering mind during Shavasana. But the correct thing to do during this 3-10 minutes is to relax the body and mind. It's hard but it's what we're trying to achieve, for at least a few minutes.
What I do is I (really) listen to my own breathe. I keep myself conscious by feeling my abdomen raising and flattening, feeling the air flowing to every part of my body nourishing every cell. I feel relax as I have no time to think of anything other than my breathe, just enjoy the feeling of letting go.
Keeping our mind empty once in a while helps bringing in new thoughts.