Think creative writers don't have to work on business writing? Think again. It's as important (or maybe more so) to have a well-crafted query or cover letter as it is to have a manuscript that's as flawless as possible. Do you have a blog or website? If not, you need to rethink....a web presence is a great tool to help you get your foot in the door. After your foot is there, your blog or website can help you with your promotion efforts.
Here is a great blog entry on the Urban Muse website on crafting a query letter (it was written with freelance writers in mind, but apply the tips to your manuscript query.) Had your query rejected? Don't take it personally: here is a blog covering the context of rejection on an old post on the Slushkiller website (thanks to Et in Arcaedia, ego's post for pointing it out.)
Tips for making your blog reader-worthy can be found here at the Write to Done blog.
Polish up your business writing and you'll soon start seeing results. Just make sure that your manuscript is completely proofread and in as perfect a condition as you can make it--don't waste the manuscript requests you receive from agents and editors.