There should be a covering letter detailing exactly what position you are applying for. Many companies are recruiting pilots at several different levels simultaneously, and you need your CV to go into the right pile, so don't say you're applying for an F/O position if what you actually mean is (for example) a cadet-entry F/O position. The experience requirements for the two positions may be quite different. The covering letter doesn't need to say much more than this. If you have something interesting (and brief) to say about why you're interested in this particular company, by all means include it, but don't feel that you have to schmooze in the covering letter.
Please bear in mind that the process we are advising you on is the entry to an airline as a prospective first officer. Other flying employment may well require a different approach, and the smaller the company the more different it may have to be! Nevertheless, as Pete says, you need to impress with your CV as briefly and succinctly as you can. It should take very little space to indicate why you are qualified to, for instance, be a glider-tug pilot. Don't bore your reader.
Scroggs