The quality of the cover letter is essential, as it is a roadmap to your petition. Take care to go into detailed descriptions of what is included in your petition, and assume that the USCIS examiner does not have a comprehensive knowledge of the arts industry. In addition to providing an itemization of the contents of the petition, the cover letter should provide brief background information on the petitioner, background information on the individual or group and details regarding the proposed activities.
Remember that the cover letter is your opportunity to make your case for the individual or group’s eligibility for O or P classification. USCIS officers are not inclined to wade through voluminous amounts of support materials, so the cover letter should include excerpts of quotes from articles, background information on the awards and honors, thorough discussion of the events, etc.