ok here goes... basically it is combining the armlock w/ a choke by simple placing your right arm across there neck gripping deep in the lapel palm up fingers inside the gi..
assumming i got into position i would have my left hand controlling his wrist. my right hand is deep in the collar with my forearm against his neck starting the choke. i have scooted out to the side and my right leg is just under his left arm pit pushing him down and my left leg is over his head pushing his head down into the choke. it should look exactly like a classic juji from the guard only with my right arm crossing his neck and choking w/ the assistance of my left leg.
if the arm is sufficiently trapped raising my hips should get the submission very quickly or i could roll towards my chest to get the arm to pop as well.
getting the choke seems much easier at this point if i get my right arm into position. all i do w/ my right hand is the same motion used in gyaku jime or very very close to it and my leg does the rest of the work forcing the head/neck into the forearm.
if my opponent drives forward trying to stack me i roll towards my chest and i will get the armlock (hopefully)
if he tries to pull away i use my legs to 'plop' him over onto his back and try for the armlock from his back if i dont have it right away i transition into a pin and keep the arm trapped. if he is using that arm to try to escape from the pin i have a good chance of falling back into the armlock or 'diving' across his body onto my chest and getting the arm that way.
Judo_tom, it would be nice if there were a way you could include like mini vids or screen caps with posts like this. Make it a lot easier for a newb to visualize.
it's hard to imagine it from text
but in answer to the post yes I do or will try to armbar from the guard whenever I get the chance
(I assume you mean me armbaring the guy in my guard as opposed to armbaring some guy that has me in his guard which I think would be tough)
You can do this gi or no gi, just flip where your hand is holding next to his neck, where you would have palm up in the lapel, palm down no gi. A great way to control oponent when in your guard.
Oh yeah, and if you are going for arm bar remember to use free hand to either grab gi pants of leg closest to head or wrap arm around ankle and put hand behind head for no gi. This is for sport, street fight different story.