If it's the same as a cross-hand choke, I perform mine in one of two ways.
If I want to cut off blood flow (so really more of a sleeper) I grab the individual's collar with both hands. However, my hands are crossed at the wrist (thus the name). The grab has to be deep enough to make up for the fact that clothing tears or stretches. The knuckles are then rotated inside, turning into the person's carotid arteries on either side of the neck. I dig inward to cut off the flow of blood to the brain.
If I am doing a true choke it is much the same except that I cut into the trachea, cutting off oxygen flow to the lungs. Both attacks can also be done from behind the person but there I usually use the clothing itself to help wrap up the lock.
Both are effective if done right but it can be hard to cinch properly. The wide variety of clothing creates variables.
The best thing, as with many locks, is to go deeply. It's easier to slide a lock back out that it would be to fight inward if you fail to get the proper depth.
