When I first started this process of getting my book published, I knew very little. I had heard about query letters, but my work as a freelance writer did little to prepare me for the importance of getting your pitch just right. Don't be surprised to find all sorts of advice when doing a Google search for query letter help. Some sites will want you to pay them to write or edit your query letter. However, after a few drafts and help from some good online resources, you should have the perfect letter ready to send out to literary agents and publishers in no time.
A literary agent recommended this site to me and I'm hooked! The blog posts query letters sent in and dissects each letter. It's great for spotting common mistakes and finding out what is considered a major faux pas in the literary world (like submitting to agents and publishers simultaneously). Read through all entries before sending in your letter to be featured on the blog.
This blog is written by an agent from the Nelson Literary Agency. The Blog Pitch section of the site analyzes book pitches from successful novels and why they worked. The goal of the query letter should be to set the tone of the novel without providing an overall summary of the entire book. Other sections of the blog delve into royalties, book promotion, negotiations and requesting submission materials.
This site has plenty of articles on how to perfect your query letter. Some of the information is general, but you can find a few nuggets of wisdom amongst the articles that talk about getting your pitch noticed and what will get you a form letter straightaway.