Until a couple of years ago, I encouraged my students to make an introduction and say it before you get into detail. But now it doesn’t seem to be the best way to improve your score from three to four (Each question of the Speaking Section is to be rated on the scale of four with four being the best.) In order to be successful in the speaking section, the best way is to make a list of important ideas.
Therefore, it would be a waste of time if you say,
The reading passage provides a general idea of archaeology, based on which the lecturer provides some examples of recent findings.
You just wasted 20 words.