After wading through hundreds of query letters/submissions/cover letters (and that's just in the past few weeks) I have realised that my attempts at providing helpful hints to writers have either:
(a) been ignored
(b) not been read at all
(c) been misinterpreted as suggestions only, when in fact they are dicta.
So, writers, I'm trying again, to save myself and agents everywhere from the task of having to penetrate several paragraphs of a letter that don't, unfortunately, tell us much about the manuscript it's attached to nor give us reasons why we should read it. And we want to want to read it - we really do. We are reading submissions because we are trying to find great writers and great stories. We just find that when you send us unclear letters, we are more likely to reject you than request your full manuscript, simply because we're seeing hundreds - thousands - of these letters each year and it all gets a bit overwhelming. Make it easy for us. Make it easy on yourself, because the process of writing the letter should also help you work out if you can describe your story clearly - and if you can't, that tells you something about the story.
Your query/cover letter should clearly state, in the opening paragraph, without too much ancillary text:
1. The title of your work.
2. The genre - or, if you can't define the genre, just say that, but then clearly describe the storyline so that the agent or publisher can attempt to guess a genre.
3. The word count.
4. Ideally, the reasons why an agent or publisher would want to read it - but we don't expect you to have a 'perfect pitch', we just expect you to be able to state clearly what's good/different/appealing about your manuscript, and to do it in under 1000 words.
In the following paragraphs, give a short description of the story - not the whole synopsis - and provide any other information that is relevant (e.g. if you are a journalist writing about a subject you've covered for years; if you have had short stories published; if you're a member of a writers' centre or association).
Your query/cover letter should not state, especially in the first paragraph:
i) That being a published author is your dream - this is assumed.
ii) That it's taken you X number of years to write this manuscript and you hope it's ready now. The amount of years it takes to write is not a badge of honour, it's just a fact.
iii) What you think having an agent will do for you and how it fits into your dream of winning an Oscar and the Booker Prize (you'd be surprised how often there are variations on this theme).
iv) That you are the world's greatest undiscovered/unpublished writer and I'll be sorry if I don't take you on (this one also turns up a surprising number of times).
If you are still in doubt about your letter, try this helpful game.