Really, if you are in a mount I suggest a straight choke, put your forearm on his throat and just lean your weight forward so that he starts to choke. In gi grappling I actually grab the inside of his collar, which makes it alot harder to get my hand and my weight off of him.
Ive found that unless you overpower the other guy this doesnt seem too effective because they can push the arm out a little bit, then they have one of your arms and can go for the escape. from mount i personally prefer the straight armbar just because its hard to get out of once you have it sunk. keylock is good too. just my personal experience, not meant to be a discredit to the advice.