Consider your field of study. Every field of study has several different journals publishing information pertaining to that field. Knowing the names of those journals narrows your prospective playing field.
Peruse the journals related to your field and identify their individual focuses. Each journal will have its own focus, though they are all in the same field. Knowing which journals focus on what narrows your focus further.
Select two or three journals with a focus similar to the content of your manuscript. While you are likely only going to be published in one, preparing multiple choices keeps you from having to duplicate the selection process immediately following your possible rejection.
Locate the contact information for each journal and any information pertaining to submissions. Make sure you get the most recent information, as the names of editors and submission policies can change over time and without warning.
Go over your manuscript to ensure it is formatted according to the submission guidelines, paying special attention to the references/bibliography, formatting and citation style requested. Sending a manuscript formatted in Modern Language Association (MLA) style to a journal requesting all submissions be in American Psychological Association (APA) style is a quick way to receive a rejection.
Create your cover letter. This should include the name of the editor to whom you are sending your work, if available. While you want to be personable, you should avoid being too personal. This is a business communication, not a letter to your best friend. Be sure to keep it professional. Include contact information for the editor in case he should wish to speak with you about your work.
Submit your work. This could be done physically or electronically, depending on the submission guidelines of the publication you are sending to. In the case of electronic submissions, some publications will take attachments; others will not. Be sure to send your work in the right format. If you are sending it physically, include a self-addressed stamped envelope, either large enough to return your work in or just large enough for them to send you a letter.