how does Shakespeare make the opening of the play dramatically effective?
Usually, in a very big way-with very little words--more succinctly-
In a Word. How many plays begin with the word 'Now' ? Small words such as, If, now, and, but, for, etc., are put to great use as attention-getters, both at the beginning of plays and the beginning of scenes. It behooves an actor to take note of these small but powerful 'notes' and let the energy from the initial opening operate as an undercurrent that drives the rest of the line, and supports (while initializing, to a certain extent, in itself) any further dramatic accentuation that may be ahead; many times expository, with a tendency to flag while the actor 'sets the scene'.This is one reason why attention to vocalization & projection are important initial components.