Your friend could do several things as described here and in this topic.
First of all, he has to stay calm. It sometimes sounds easier than it is, but it is pretty important. He could spin around his own axes, rub his hands (or touch anything else for that matter). He could also grab something from the dream. For some people it works to focus on something in the dream.
I don’t think it really matters if you’re a light sleeper or not. He should be convinced that he doesn’t wake up at the moment he realises he is dreaming though. Because otherwise you might get the effect that you wake up, because you expect to wake up.
Congratulations with your own Lucid Dream. 
I hope many more will follow.