A well-written, properly formatted cover letter is the first impression an editor of a journal has of the submitting author. Make sure that your cover letter is free of typographical errors, misspellings, casual language, and any other idiosyncrasies such as a nonstandard font. A good cover letter will ensure that the content of your article is given serious consideration by the journal's editors. Make sure your cover letter is brief and direct (usually no more than four paragraphs, maximum).
In addition to adhering to any journal-specific guidelines, make sure your cover letter follows the following guidelines.
Gump (2002) recommended that authors establish their credibility by using institutional letterhead if possible, as well as using a title or appointment to help establish qualifications (e.g., "Associate Professor," "Visiting Professor"). Gump also advised that those not currently affiliated with an academic institution use the letterhead of their company or organization. Of course, if you are submitting electronically, it may not be possible to make use of a letterhead.
Establishing your authority must also be done in the body of your cover letter. Be sure that your cover letter makes clear to the journal editors whether your research fills a research gap in your field. There is no need to tell the editors that your article is going to change the world; avoid hyperbole and state simply and briefly the contribution that your article contributes to your field.
Gump, S. E. (2004). Writing successful covering letters for unsolicited submissions to academic journals. Journal of Scholarly Publishing, 35(2), 92–102. https://doi.org/10.1353/scp.2004.0007
There are several ways you can personalize your letter to establish a connection with the editor and the journal. These ideas include making a specific reference to a previously published article in the journal that contains similarities to yours or demonstrating a familiarity with the interests of the journal's readership.
Different journals have different rules about what types of submissions they will accept. A simultaneous submission is a submission that you have sent out to more than one journal at the same time. Many journals have stated policies that ask submitters to only submit to one journal at a time. Polices regarding simultaneous submission often vary by field. For example, most journals in the sciences require that papers under review not be submitted elsewhere, while some journals in the humanities have different policies. Be sure to check each journal's submission policies to determine whether they accept simultaneous submissions or not.
If you do submit to a journal with a no simultaneous submission policy, include a line in your cover letter informing the journal that your article is not under consideration elsewhere. Breaching this rule and submitting to multiple journals that explicitly request exclusive consideration is widely considered unethical in the scholarly community.
Previously published material: Without exception, academic journals will not publish previously published material. Therefore, you will want to make it clear to the editors in one brief sentence that the article you are submitting for consideration has not been published elsewhere.
Funding: If you have received a grant or funding in order to conduct your research, be sure to mention the source of your funding in your cover letter.