As you have probably guessed, using the cross collar choke to set up an armbar from mount is remarkably similar to setting up the same transition from guard. Threaten the cross collar choke and then isolate his elbow when he moves to defend. Making this connection, especially if you are new to jiu-jitsu, helps to solidify the pieces that make an armbar work while also laying the groundwork for a strategy-based approached to grappling. If you see how two techniques connect, and can use the same two techniques in two different positions, you have started to form a web of attacks with which to ensnare an opponent. That web might be small, but learning how to build such webs on your own is far more valuable than a large collection of individual techniques.