There's no point in trying to be sophisticated about this: the crisp sarnie was part of most people's youthful gastronomic delinquency, and is one of the great communal eating experiences.
Still, there are rules that should ensure an above-average result. One, only soft white bread of the Mother's Pride variety will do - the textural contrast between the two primary elements is crucial to the success of the finished item. Two, the cheaper the crisp the better - the higher tensile qualities of hand-turned chips are not suited to the evanescent fragility of this delicacy. Third, there is the matter of additives, by which I mean butter or mayo spread on the bread, not to mention the inclusion of other vegetal matter - eg, cucumber, cheese, thinly sliced Mars Bar, etc. Here, I think, personal values have to play their part. I've experimented with peanut butter (horrid), Marmite (heaven) and caviar (bliss).