Only submit to one journal at a time. Most medical journals do not allow for multiple simultaneous submissions.

Cover letter

• Often you will be asked to submit a cover letter along with you manuscript
• Cover letter is only seen by the editors (not the reviewers)
• Summarize how this study builds upon what is out there
• Give context to how this fits in with current science
• Do not copy & paste your abstract
• Opportunity to communicate to the editors at a more personal level

Reviewer suggestions or exclusions

• These can be included in the cover letter
• There may be other opportunities to provide this information during the submission process
• Editors take these suggestions very seriously
• Can suggest reviewers based on what kind of expertise is required
• Can suggest names to exclude as reviewers due to conflicts of interest, etc.

More info: International Committee of Medical Journal Editors Recommendations for Sending the Submission