Serve and volley in singles play was endangered for a while. It is definitely down but not out - you still see it occasionally. Like the lob, it is a rare event in professional tennis. But to the 99% of us who don't play professionally, and the majority of aging players trending into doubles, it can be useful. So put this drill in your tool box. If players are not using S&V, we don't want it to be because their coaches never taught it to them.
Serve and volley just means you pair a serve with charging into the net to play the next ball from there. Sure, you are taking a risk by leaving the back court open, which is why you want to deploy this at the proper time. But worrying about the 'when' is for another lesson. Attack and Smack is more about the basics of getting into the mindset of moving in behind your serve. This is so often an anomaly to players who are trained to recover and maintain a baseline position.
Your players will need to be advanced beginners or beyond. The concept is simple: server must serve and volley after every serve, or serving team loses point. End of story. Note it is easy to forget the serve and volley aspect until you have played out a few points. We are all so focused on point outcome, and rightly so. But for this game, make sure all players understand the point is lost if the server does not serve and volley, regardless of who actually wins the point.
From The Tennis Drill Book by Tina Hoskins.