Sometimes people have a knack for writing their own query letter. Often they don’t.
It’s not because they can’t write well; it’s because the query is a sales tool and few authors, fiction or nonfiction, are trained in sales techniques.
Queries have a second obstacle built in: until an author is published, they often don’t know what the publishing industry expects them to include in the query or the book proposal. They don’t know the buzzwords, they aren’t sure how to position their work in the market, they don’t know what trends are current and what is fading rapidly away. The mistargeting of only one of these items is enough to make an agent or publisher stop reading and move on to the next query.
Practice is fine. Publishing industry savvy is much, much better.
Display natural talant by:
–Reading industry publications: Publisher’s Weekly, Writer’s Digest, etc.
–Read industry blogs: Huffington Post has several, and up-and-coming authors often blog about their experiences.
–Subscribe to industry newsletters. Publisher’s Weekly has a free e-newsletter, as does Writer’s Digest. There are tons of free e-newsletters out there. I sift through a few dozen every week.