The force essence is entirely separate from the forces of good and evil, light and dark respectively. The standard intergalactic biped however, is often ignorant of this fact. The peasants of the universe think of the light and darksides as using their own seperate magics, and therefore one magic must be powerful than the other. They know not the ways of the force.
My dear missionary, you must capitalize on this ignorance. Often whilst converting speak of, "The power of the darkside." The general populace has an intrinsic fear of the mysterious, and you must continuously label and enforce in their minds the idea that the ways of light are mysterious and hard to learn. The darkside, fueled by reflex emotions, is a natural course and should be followed.
Furthermore, it is of paramount importance to emphasize that the light side requires a leap of faith; the light masters promise that learning takes time, and you must trust them, trust that eventually you will wield their power. The dark side requires no such faith. You can see its power right before your eyes. Point to the great works of art of times past, and how they were influenced by passion and human emotion, not promises and premeditation. The greatest works were spontaneous. Their ignorance and inability to question will certainly leave them agreeing with you by this point, and by this very step they will be joining the darkside. For they're using their emotion, their desire to be part of something larger than their miserable lives, to believe you, rather than applying reason and questioning if the greatest works were impromptu. Your victim will even think that he's avoiding blind faith, while in fact he is jumping into blind ignorance.
Offer explanations for what they see in human emotions. Explain that war is needed to keep the machine running, that restriction is needed to keep an order to things, and when they are ready, reveal the secret of ignorance.
-Taken from the archival papyrus scrolls of Emperor Palpatine