Start out getting your first collar grip nice and deep, with emphasis on keeping your wrist straight. If your wrist breaks and wraps around your opponents neck then you lose the force of the choke later on. So nice deep grip on the first collar, then reach under and get your grip on the second collar nice and deep, and turn your thumbs towards each other and pull your elbows down to the mat.
If you can't get the second grip because your opponent keeps blocking your hand then go for the grip 2-3 times then swing your hand over the top and grab the gi near on top of the shoulder as close to the neck as possible. This finish requires slightly more strength since you are having to close a larger hole for the choke, but it his essentially the same, turn your one thumb in and then elbows down.
If you can't get that grip either then you wrap that arm around on the same side as your first collar grip and pull your opponent down, breaking their posture. then you slide your second hand across the back of their neck and tuck your thumb into the collar right behind their ear. Then as they try to posture up you clear the head, turn your first thumb in, and pull the elbows down to finish. This one is super tight.
If your opponent doesn't try to posture up, but just clings to you there then you hip out a little bit and reach straight across your body, still holding the first collar grip, and place your elbow on the opposite side of your opponents neck, then scissor your elbow and your gripping hand across. This one works really well once you figure out the proper elbow placement. You really have to make sure you get the elbow on the neck to get the tap.
Running through this sequence is highly likely to secure you a collar choke.
I had everyone drill by one partner being in closed guard and the other person running through the sequence ONLY trying to get the collar choke, no other offense, while the top person only tried to defend the collar choke, no guard passing or anything.
After that we did some flow rolling, then Kris wanted a competition level roll. Right of the bat I punched him in the mouth. Not intentionally, but grabbing for his collar, yanked him into guard and just climbed up him and secured the chinstrap choke which I'm beginning to prefer as my single collar choke variant because it's harder to resist. The only difference between it and the normal single collar is the angle that you put pressure on. Chinstrap involves pulling "up" towards the back of the head at about a 45 degree angle compared to the chin. That pulls the collar up into the crook of the throat and makes it MUCH harder to tough out.
Second go he stood up, so I stood up until I could get a sleeve grip, then pulled guard, swept him, and kimuraed him. I liked the level of intensity I kept during those rolls and I hope I can harness it during Lutador.