How is the human body plan and a fly body plan similiar?

Although they are in different phyla--humans in Chordata and flies in Arthropoda--both have a great many similarities in their body plans.

Both are bilaterally symmetrical; that is, there is one and only one axis that can "divide" their body in half. The right side of a human's body is the mirror image of the left; the same is true for a fly.

Both the human and the fly have cephalization--their major sensory organs for sight, hearing, taste, etc., are at one end of their bodies (the head).

Both humans and flies are coelomates (or eucoelomates, in some texts). These animals have a "true" coelom, or body cavity, that contains organs. They have three cell layers--ectoderm, mesoderm, and endoderm. These embryonic layers become different cell types and organs. Other types of animals have no coelom, or a pseudo (false) coelom.

A difference between humans and flies in their body plans is that humans are deuterostomes, and flies are protostomes. This means that the first indentation into the developing embryo becomes the anus in humans, and the mouth in flies.