Let's start first with first sentences.
It seems to me that a good deal of time is spent in writing workshops talking about first sentences. Which is, I believe, as it should be.
You need only consider how many novels and stories can be identified by their first sentence alone in order to appreciate the importance-the burden and the opportunity-of a first line. Proportionately speaking, I don't know that there's another art form that can be so readily recognized by so small a sample.