Hi Mary: There is currently a lot of discussion on this topic. I will give you my view, but keep in mind that there are other views that you may hear.
My view is that in an otherwise warm to hot and humid climate you should not install a horizontal vapor barrier. The reason is that you want moist air that naturlally rises, to keep rising (the moisture that is), and be passed through a well ventillated attic. Horizontal impenetrable vapor barriers, like sheet plastic, are a definite no-no, as they will just collect moisture on their upper side that eventuall become pools of water.
By all means, insulate your attic space well, taking care to hand-pack insulation around the openings into the attic like pipes, wires and other intrusions. But also be sure your attic is well ventillated to keep moving the hot air that can get trapped in an attic.