Compose a brief, specific and compelling query letter or proposal letter.
Open with a sentence that describes how you categorize the work (sports, romance, etc.) Then briefly state the manuscript's premise and its key action/character(s), usually in two to three pages or less. Detail why you're qualified to craft this work, and why it is important for this publication to consider. List your most relevant previous work, and include a CV or an online link to the same. Conclude with some words on why your work should be given attention amid the other submissions. Be sure to thank your addressee, and include your name and contact information.
In your manuscript introduction, launch the story's action and key character(s) immediately. A manuscript's first five pages often can determine if an editor will choose to read through the end. Avoid telling the backstory at the beginning of your manuscript. Instead, let the editor follow the main character through a day that is unique or crucial. Show the editor how that character acts during a moment of crisis, or while "on a precipice."
Concentrate your manuscript on one distinguishing factor, and let your characters show on the introductory pages. To get an editor's attention, your submission needs to contain specific, remarkable details -- both about the story and about yourself.
Work up some bravado and don't be afraid to proclaim what your writing strengths are. If description or dialogue are your strong points, then showcase those strengths in your manuscript summary. Show strong conviction as a writer, yet also show a willingness to work with an editing team on your writings.