By reading sample cover letters, you can get a feel for the appropriate tone of a cover letter, and a template will show you the proper formatting. (thebalance.com)
The overall tone of your cover letter should border on formal and informal — a little bit of both at the right time will serve any situation well. (coverlettersandresume.com)
You'll also want to see that the language and tone of your cover letter mirror the tone and language in the cover letter. (cover-letter-now.com)