Effective communication is critical during the job search process, both your verbal communications (in-person or over the phone), as well as through all of your written materials and correspondence.
The Professional Correspondence chapter from the Career Guide (starting on page 62) provides guidelines, tips, and best practices for writing:
Cover letters (e.g., "how to" guide, including samples)
Thank you notes (e.g., how to write them, when to send them)
Professional References
Other forms of professional correspondence (e.g., follow-up emails)
Also available to you is the Free MasterClass: Build a Resume + Cover Letter that Wins Interviews
Cover Letter Packet - Defines the purpose of cover letters, best practices for each paragraph, and includes samples.
Cover Letter Visual - Breaks down each segment of the cover letter.
Cover Letter Workshop - Workshop presentation materials with a high-level instruction for writing cover letters