1) If you’re querying an agent or an editor, and you admire an author they represent or edit, say so. “I am querying the Stuart Krichevsky Agency because I love the work of Sebastian Junger and aspire to his level of nonfiction writing” is acceptable and welcome.
2) Tell us your writing credentials . . . “I have published articles and stories for children and adults in Crow Toes Quarterly, Kiki Magazine, Six7*8th, Bird Watcher’s Digest, Lighthouse Digest, and Tennis View Magazine, among others. I have also won awards for my children’s and adult writing in six national contests.”
3) . . . and about famous/influential people who will support your book. “My wife is a writer for AP and can get us coverage,” and “Our neighbor Jamie Lee Curtis has promised to feature the book on her blog” are very useful for a publisher to know!
4) Sure, if you have a strong social media presence, let us know. Your publisher will be inquiring into what kind of social media following you have anyway.
5) Know your market! Your editor/agent will have to slot your book into a niche that’s out there, so it helps if you can do that for them, being careful, again, not to compare it to the megahit of the moment. “My book aims for the Sarah Dessen fan” or “It has the old-fashioned feel of The Penderwicks series” are examples that work.
Above all, just tell us a little bit about your book, and, as I said above, whom it’s for, what other title(s) it may be like, and if you’ve published. That’s all we need to know to get us interested. Good luck!