This is a basic setup for an armbar from guard. It is a good setup for beginners to learn the critical points of this technique and to make it a tight move with as few gaps as possible.
Ming is in my guard and defends by pushing my hips down with his hands. I reach accross, grab his wrist and my other hand grabs his ellbow on the same side. This makes it difficult for Ming to pull his arm out.
After having secured his arm the next target is to bring his ellbow accross my centerline. However, even with two hands on one his arm this might be difficult. I therefore bridge and build a slope with my body to make his hand slide more easily accross. Note that I start to pull the arm when I drop back, which decreases the pressure of his hand on my body and make him "fall into a hole"
As soon as Mings ellbow passes the centerline I have to secure it in this position. I therefore release my grip on his wrist (but keep the hand on the ellbow) and pull his head down to stop him from posturing out. I put my left leg at his hip and place my thigh behind Mings ellbow/shoulder to block this escape route. With my right leg I reach as high as possible accross his back to keep him down. Note that I swing my body around by almost 90 degrees to the right to achieve that.
I keep pulling Mings head down but simultaneously start to push his head to the side to get space for my left leg. I bring it accross his neck and cut down with my calf. His left wrist is caught under my right ellbow (that happens frequently) and it is now sufficient to arch slightly back to get the tap. Note that my left hand never leaves his ellbow and that I maintain a crunching position from the moment I secured his ellbow until the end.
If the wrist of your partner does not get caught under your ellbow simply use your hands to control it. If you have to roll your partner onto his side/back to finish, this is an indication that your control of his ellbow and upper body is not tight enough.
Okay, this is a flashy move. It is unlikely to work against a more experienced opponent but it is a fun move and certainly spectacular when successfully applied.
I start in butterfly guard and aim for a sweep but Chris is resisting by getting on his feet and pushing forward. I put my hands under his armpits, transfer my feet to his hips and lift him up. Note that balancing your partner/opponent in the air is more difficult in slow motion (as demonstrated here) than in a dynamic situation.
To get into armbar position I release my left foot from Chris' hip and use my right foot at his hip to push myself around by about 90 degrees. The left foot swings around his head and at the same time I change the grip with my left hand to control his ellbow.
Without the support of my left foot Chris drops down to his right side and I finish with a classical armbar.