I’ve generally kept them succinct, unless there’s specific information you need to provide which isn’t on your CV (and arguably, if it’s important, it should be on there). So something like,
Dear Sirs,
I’m writing to you in response to your job vacancy ref 123 as advertised in the August edition of Ski Resort Jobs Monthly. I would like to submit an application for this role as I believe that it is an excellent match for my skill set. Please find attached a copy of my CV for your consideration.
In addition to the skills and experiences listed on the CV, please be advised that I am keen and enthusiastic, a hard worker, and know 47 different words for “snow.”
I look forward to hearing from you soon,
Yours etc.