I used to do hiring in IT. I paid attention to how well written the CV was, how believable it was, and the content had some relevance - though less than you'd think. I'm not sure if I was shown cover letters, since I was on the technical side of things, my job was mostly to make sure they weren't full of shit.
Don't be full of shit. I'd have hired someone who knew they were smart but inexperienced over someone who knew the terms but couldn't go into detail about a subject.
Honest is good. Ambitious is good. Confidence is good, but stay away from cocky.