In any inverted flight the rudder direction is reversed from upright flight. Therefore, for a negative snap the rudder direction must be reversed.
For a correct snap, the elevator input is started first to stall the wing before the aileron and rudder contols are input. The goal is to just see the nose break in the snap direction before rotation is started. The use of the elevator control first helps hold the airplane on its desired flight path. You will find that elevator input must be maintained during the snap. The amount of elevator can be reduced during the snap to assist in maintaining the original flight path.
John