In “How to Write a Cover Letter that Gets Read,” Jason Cohen provides an excellent and thoughtful tutorial for job applicants. As to his recommendation to use “personal, not formal” language, I would counter that you can be both polished and personable. If you follow certain conventions to keep your language polished (no contractions, no casual and overused adjectives like “great” or “amazing,” full titles instead of acronyms, etc.), then your tone can be more personable and open. Of the hundreds of cover letters I’ve revised, I would say that only a small fraction have erred on the side of being too formal; most are much too casual, which can come across as overconfident or uninformed. If you are a college student applying for an internship, it is also crucial to mention that you hope to prove yourself worthy of a full-time job offer after graduation, as the company is hoping that the time and cost of training interns will be worth it to them in the long term as well.
For Jason Cohen’s advice, visit: http://workawesome.com/your-job/how-to-write-a-cover-letter-that-gets-read/