A well-crafted cover letter is essential for virtual assistants seeking work on Upwork, as it introduces them to potential clients and showcases their skills and experience. The document provides tips for an effective cover letter, including personalizing each letter, highlighting relevant skills and qualifications, backing claims with examples, maintaining a professional tone, and including a strong call to action. Following these tips will help virtual assistants stand out and increase their chances of landing desirable projects on Upwork.