If you're in a gi, get a decent cross-collar grip, and punch your fist into his throat. This will keep him looking away. Hip out to the side and threaten his back (grab belt, gi pant leg, or farside armpit). If he dangles his arm out to try and grab your belt to line up again, you may be able to get the armbar.
Also, if you think you will be falling into a poor position, don't be afraid to shrimp, or butt scoot away before the pin occurs. Most beginning people wait too long and try the escape when the sidemount/mount has already been established, do the same escape as they are trying to get the hold-down and it'll be a lot easier.
Also, if you think you will be falling into a poor position, don't be afraid to shrimp, or butt scoot away before the pin occurs. Most beginning people wait too long and try the escape when the sidemount/mount has already been established, do the same escape as they are trying to get the hold-down and it'll be a lot easier.