..Stay strapped in and wait for the violent movement to cease before releasing your seatbelt and escaping (if you have kept a hand holding on to something that will help you find your exit).
Close, but no cigar. You must remain strapped in and form your exit (jettison door or push out window) and be holding on to a known reference (eg, the opening) before releasing your seat belt. And then only after all the violence has stopped. If you are submerged and just release your seat belt you will become disorientated and have no way of knowing the way out. A passenger walking in off the street and taking a jolly has very little hope during a ditching, unless the floats inflated and the aircraft remained upright (eg the Hong Kong accident where all passengers survived). If they can't swim, even less hope (because they will panic when under water).