Address the letter to the correct recipient (and make sure that the name of the person is also spelled correctly). Some publishing houses might not list the name of the editors who actually read manuscripts—if this is the case, address your letter to "Dear Sir" or "Dear Madam." Or even better, address it to the editor to avoid gender mistakes.
Make sure that the name and address of the publishing house is correct. This will ensure that your cover letter reaches its destination.
Include information regarding the name of the novel and a summary of what the novel is about. This will give the editor a general idea of what to expect from the novel. The summary should be only as long as is necessary to include a general idea of what happens in the chapter, but try to limit it to one or two paragraphs.
Include any and all biographical information that's relevant to the submission. For instance, information regarding educational background or previously published credits are relevant. If you have no previous publishing credits, it's fine not to mention any biographical information.
Mention how your novel will fit in with the publishing house’s repertoire. Mention any other novels similar to yours that that were published by the company: This will let the editor know that you researched the market and know the company well.
Conclude by thanking the editor for her time and convenience. Include any information regarding materials mailed with the cover letter, such as the manuscript and return shipping materials.