My advice to authors: After putting a lot of time and care into creating your manuscript, take time to learn the proper way to present your manuscript to the right agents or publishers. Research. Make sure you know to whom you are addressing your query and that it is someone with an interest in your genre, target audience, and writing style. If you do not, you are wasting not only your time and resources, but the time and resources of the people to whom you submit your work. They will not waste a lot of time, however, as a glance can tell them whether you were unprofessional, impolite, and/or ignorant of the publishing protocol. They don't have to read the entire submission to tell whether your writing is amateurish or that your work does not fit their needs.
I present workshops on manuscript submission that goes into greater detail and gives opportunity for practice in writing query letters, cover letters, and synopses. After receiving two submissions yesterday, I just want to point out a couple of the basics. First and most important, be sure you have a well written manuscript, synopsis and query. Secondly, don't waste your time sending to those who will obviously have no interest in your subject or genre. When you find a good fit, use professionalism. Address the agent or editor by name, spelled correctly. Give them what they ask for. Submit by the means they prefer.
As stated in my submission guidelines, I prefer queries by e-mail and I want a synopsis and the first chapter. Yet, I often receive entire unsolicited manuscripts via snail mail. Too often they come without a self-addressed stamped envelope. If you send anything by mail always include a SASE, a reply postcard, or both.
Like most editors or agents, I'm pleased to receive submissions of well-written queries introducing the type of books I publish, and I'm disappointed and/or irritated when I receive unprofessional queries. My name is not "To Whom It May Concern" and most likely what you are sending to that name will not concern me at all.