Watch the following video for details from Americana instructor Zack to help you finish the cross-collar choke from the back:
And when your opponent starts to defend the choke, it will open up two alternative attacks for you –
1) switch your hooks, shift your hips, and use your existing top cross-lapel grip to set up the bow and arrow choke or
2) hook his left arm and swing your right leg up and around his head for an armbar.