As someone pursuing a job you are both salesman and product. The potential employer is your potential customer.
Am I what they need?
This is the single biggest question. It's fine to not have certain requested certifications, degrees, experience, etc. so long as you are capable of fulfilling the role in which they are hiring you. (note: some certifications are legal requirements)
I don't want them to "consider me" I want them to "desire me"
As a salesman you always push the good, you avoid the bad as much as possible without treading into what could be considered cagey or dishonest. You don't want your potential customer juggling the your pros and cons on whether they even want to hire you, you want them to think "if I hire this person they are going to make me money". You want the only thing standing between you and a pay check is your competitors (other potential hires) potentially having a better offer.
Think of your cover letter as your opening pitch. You want to intrigue these people, you want them to see the best you have to offer and why they NEED you. Think of this like you when you're buying a car or computer. You give the bird's eye you tell them why they need you specifically, and why you are reliable (IE that you want to work for them)
Think of this as a tailored spec sheet. You're still pitching yourself, but if you didn't get that hook in already odds are they'll skim over it with little thought. If you have them excited they're going to look over this carefully and if everything is in order want you even more. In your CV you want to highlight the best you have to offer, what you've done to help your past employers (experience), what skills you offer (self explanatory), what documentation you have (certs/degrees) to confirm you're legit. You want them to finish your CV thinking you're a solid option. Where the only thing that could stop you from getting the job is if someone simply out sold you both on their pitch and what they backed up on paper.