First thing you need to do is stance drills. Get those balanced stances and circling under control before adding anything else to the equation. If they can't move and stay on balance, they'll never learn to take a proper shot or execute a proper sprawl.
Next, you introduce the shot walk. Obviously, 90% of the guys will have issues early on with the concept of falling on their front knee, so give them tricks like the 'split step' to help them lower their level and to make the initial penetration step a little less heavy and off-balancing.
After making them walk all over the mat in their stances and making them do their shotwalks in lines back and forth across the mat (this is the time for you to watch each athlete and trouble shoot with them), it's time to pair them off and make them actually perform a double leg. Emphasize things like penetrating with their foot actually between their opponent's legs, the concept of impact and off-balancing the opponent with the shot, and the idea of leg drive and finishing at an angle.
Next, teach the sprawl. Make sure they know the lines of takedown defense: Head hands, elbows, hips, and make sure the learn the cross-face and spin. Spin drills work cardio, and reinforce the proper positioning and direction changing that is vital to good takedown defense.
This should get everyone started, and should honestly be the first several days of practice. Eventually, start adding the single leg, the front headlock, the high crotch etc. Once they have basic mechanics down, return to the basic stance and double, this time emphasizing basic ideas of hand/head control from neutral and how to make the opponent step, stand straight, fall forward (basically, everything that sets upa shot). I wouldn't even introduce referee's positions for a week or two.
Hope this helps, good luck coaching. It's a blast.
