Don’t describe what your cover artwork should be or send cover artwork with your query. While authors have some input into this, and are usually allowed to see and comment on a couple of different versions of the artwork, the publisher has ultimate say.
Self-published works: Agents receive lots of queries where authors say “I have published [pick a number] books.” But they are all self-published ebooks that only have a handful of reader reviews. There is nothing wrong with self-publishing — and I know some writers doing astoundingly well in this field now — but if you do self-publish, you need to do your utmost to market the works. Editors will interpret a book with a handful of reviews and low sales ranks as the author’s lack of platform. They need authors who can sell books no matter what the challenge is.
Please include all the information an agent needs to make a decision to see more of your manuscript. If they ask for a sample on their submission guidelines, don’t forget it. Don’t make me click through to your website for more info. A lot of websites contain drive-by malware, so I just don’t click on anything. Everything needs to be in the query. If I absolutely love what I see, I will do my own online search.
A bit about the Pushcart Prize. I get all sorts of queries from writers who had a story “nominated for a Pushcart Prize,” often years ago. Please understand that every magazine gets to nominate 6 stories per year. That’s hundreds of magazines per year, I would suppose, nominating 6 stories each. Unless the story was shortlisted for the prize, I am very sorry, it just isn’t going to impress that many agents. I’m not saying not to mention it, or if it was nominated from a major magazine that it wouldn’t be important, but if it’s a small magazine, and you base your entire bio around it…. well, just sayin’….
Social media: Sometimes I request a sample or a proposal, and then get bombarded by all these invites to follow the writer on FB, LinkedIn, Twitter, Google +, Instagram, etc. Don’t do this until you have developed a professional relationship with the agent.