A feature that I loved in the conference was the First Pages session. Editor Martha Mihalick, agent Alyssa Henkin, and published authors Stephanie Greene and Anita Silvey (who also worked in publishing) sat around a table and read random first pages of conference attendees and commented on their immediate first impression of the work.
Mine was not, unfortunately, drawn from the box to be commented on, but I still learned a few pointers about writing.
The biggest thing was how important that first page is. Editors and agents may stop after the first page. It really must grab them. In some cases, a good (or bad) first line made or broke the entire work for them. Silvey referenced Charlotte's Web's powerful first line as an example. Titles were also important—a boring title made them think the book was a bit boring.
What happened in the first scene mattered. If the character was doing something boring, like weaving, then that invited boredom onto the page. A mundane task influenced the entire scene, despite an interesting character or dialog. Just moving the boring task back to later pages helped keep the integrity of the important first page.
The most helpful suggestion is to go back and look at the first page by itself. After it is written, look at just that page: analyze the structure, the rhythm. What happens in that first page? What is the first—and last—line on that page?
A good first page seemed to make the editors/agents more willing to forgive mistakes in the second, third, etc., pages—a good first impression made them more lenient to other things in the text. Likewise, a bad first impression made them much more likely to not even turn the page and look at anything else.