The purpose of this drill is to perfect your infielders' skill against the bunt. To set up the drill, you'll need your typical infielders, though a pitcher is optional. You can double the effectiveness of the drill by having some of your other players rotate as batters - let them take turns laying down bunts. Alternately, you can simply have your catcher (or a coach) roll soft grounders to simulate bunts, but I prefer using batters.
To perform the drill correctly, you need to emphasize the importance of hard charging by the fielders. Once the fielders see the batter squaring to bunt, the first and third basemen must charge at full speed to field the ball. Simultaneously, the second basemen and shortstop must wheel to cover the corners - the shortstop covers third base, while the second baseman covers first.
Have the fielders throw to the opposite corner - the third baseman throws to first, while the first baseman throws to third. Stress aggressiveness, since a timid corner infielder might as well let the catcher pick up the bunt. Don't let them be afraid to overrun the ball, to pick up the ball barehanded, and to make throws on the run if need be.
You can of course mix things up by having the first baseman throw to first, and the third baseman throw to third, since both of these situations do show up in games. Once your players become proficient at the drill, you might want to mix in some regular hitting so that the fielders do not cheat.
Work this drill from time to time, and you'll be amazed at the progress of your infielders.