Are you about to query?
I'm offering some links to
JM Tohine's blog post on "The Biggest Mistakes Writer's Make When Querying Agents'. Here.
To Miss Snark's blog. Here. Which is a big ol' banquet of information you can return to again and again.
Nathan Bransford's advice on a couple few topics. Here. Here. Here. and Here.
And Dystel & Goderich's very sensible 'It's Not About the Details' post. Here.
I hope some of this will help you.
My own advice: What matters is the manuscript. Only that.
The rest is sound and fury, signifying nothing. You get the manuscript right and somebody will buy it.