People assume the workshop day is about prose. It is not. Twelve people bring nine hundred words each and I can tell you by the end of the first page whether the book underneath is alive, and it has almost nothing to do with the sentences.
Three things I am reading for
Does somebody want something. Not a theme, not a mood. A person who wants a thing they do not have. It can be small. It usually should be.
Is the writer interested in what they are describing. You can hear boredom. A room described out of duty reads completely differently from a room the writer has actually been standing in.
Has anything happened that cannot be undone. Not a death. A door that is now open. By nine hundred words something should have shifted that the next page has to deal with.
Openings that do all three are rare, and every one I have seen has turned into a book. Openings that do none are almost always beautifully written, which is the cruel part.