use the same, or very similar, wording as in the question. If part of the question is "Discuss recent developments in communication technology" then in your introduction say something like "This essay will consider recent developments in the field of communication technology and will ... ". Don't leave any room for doubt.
use words and expressions which clearly show the plan behind your writing, for example:
The essay is divided into four main sections.
It will first consider ...
It will then go on to describe ...
The third part compares ...
Finally, some conclusions will be drawn as to ...
The importance of introductions (and conclusions) cannot be stressed too much.