Masks on, throttles idle, nose down with an offset turn, emergency descent checklist. Make the required radio calls. Level off at the altitude planned for this contingency at the appropriate lateral offset distance. Establish planned contingency airspeed and course appropriate for contingency destination. Notify ATC as required. Hope and constantly check that your contingency fuel planning was adequate.
Hopefully your pre-flight review of the contingency planning leaves you with some modicum of confidence in your new prospects!