Sample cover letter for Internship position at Facebook

xplain why you are sending a resume. 

Don't send a resume without a cover letter.
Don't make the reader guess what you are asking for; be specific: Do you want a summer internship opportunity, or a permanent position at graduation; are you inquiring about future employment possibilities?

Tell specifically how you learned about the position or the organization — a flyer posted in your department, a web site, a family friend who works at the organization. It is appropriate to mention the name of someone who suggested that you write.

Convince the reader to look at your resume.
The cover letter will be seen first.
Therefore, it must be very well written and targeted to that employer.

Call attention to elements of your background — education, leadership, experience — that are relevant to a position you are seeking. Be as specific as possible, using examples.

Reflect your attitude, personality, motivation, enthusiasm, and communication skills.

Provide or refer to any information specifically requested in a job advertisement that might not be covered in your resume, such as availability date, or reference to an attached writing sample.

Indicate what you will do to follow-up.

In a letter of application — applying for an advertised opening — applicants often say something like "I look forward to hearing from you." However, if you have further contact info (e.g. phone number) and if the employer hasn't said "no phone calls," it's better to take the initiative to follow-