In this video I show a great Butterfly Guard Pass called the Yoke Pass. This works extremely well in both gi and no gi with absolutely no changes in the technique.
As with many of my other Butterfly instructionals it's important to maintain good posture and squeeze with the knees. This specific technique is great for when you didn't get inside head control or your opponent decided to lay his/her head on your shoulder (which I find to be very common, specifically with the overhook sweep).
The most difficult part is going to be stuffing your opponents head. I find it easiest to do this by combining a stuffing of the head with my hand with an extension/level change of my upper body. This can be accomplished by popping to your feet if you are quick or by just by extending your trunk if you're tall.
Once the head is fed into the armpit it's time to extend your legs and transfer pressure to to the shoulders of your opponent. You should have all of your weight on the shoulders and your stomach should be blocking the head movement. Although this may feel uncomfortable on your opponents neck, it should NOT be a neck crank.
Use the space gained by the transfer of your weight to walk your legs around to your opponent's back. If they grab your leg you will have a free hand to stuff it (make sure to reference the video).
Try to avoid taking your arm out of the crook of the knee until you are all the way on the back and in a good controlling position. You may feel like your arm is being bound but it will be difficult for your opponent to armbar you. They may try but you have too much control over the orientation of your elbow. The most frustrating thing will be your opponent just trying to grab a hold of that arm and holding on for dear life. If this happens there is a Crucifix transition where you can step over and easily take control