When I was involved with hiring in indie film and with studios, I'd say about 95% of the covers we received showed zero actual knowledge about who we were and what we were doing. Those are easy to discard. See how easy it is to stand out with a little time, care, and research? The vast majority of people are not very good at applying to jobs. If you are, your chances soar. A former student of mine gave this example of how she scored a spot a Pixar, easily one of the most competitive places to get into: "Before I got a production internship at Pixar which led to a full time gig, I had applied one other time before getting a call to interview. I really do believe it was because of my cover letter and how specific I was about why I wanted to work at Pixar at the time. Instead of merely saying 'I love Pixar and am a huge fan!', I thought of it from the employer's POV and from a collaborator point of view. I researched what projects were coming up the pipeline, gave specific examples of how my professional experience could support their creative projects, etc. They want to be able to trust that not only can you do small tasks like staple pages together, but they also seemed to care about why you as a living human being care so much about working for their company. Think of your cover letter as a great example of storytelling and by the end, the recruiter should know whether you'll fit into the culture/job position or not."
Your first line in a cover should be simple. What do you want? "I am applying for..." "I seek...." Second line should be one or two key lines on who you are. "I am currently a student at...." "I major in..." "I graduated from... " Then you can put in a line with your best pitch! You won an award. Or had a great prior internship. Or someone referred you to the place - "George Larkin referred me...." Second paragraph is some key details on who you are and how it fits into the position. This is also where you work in what you know about the place and/or person you are applying to. How much "personality" you put in depends on your style and where you are applying. I've seen some that showed too much, and I've read others that felt flat. It's a gentle art and can be hit or miss. Some companies like some flair, like Pixar. Others are more conservative and that same emotion will hurt your chances there. That's why it's best to research a company's culture first. Often, though, it just comes down to the personality of the person who reads it first. Remember, jobs generally don't care about what they can do for you. What can you do for them? Then a few wrap-up lines. "Thank you so much for your consideration!" "Please let me know if you need any further information..." Three paragraphs, four at the most. One page max. Header with date and your info. Apply to a specific person if you can. Some studies show people spend 5 - 10 seconds on a cover (and resume). So NO TYPOS, visual appeal, not too much text, and a clear, polite, and knowledgeable request. Send as a PDF unless another format is requested. Name file after yourself. So many people call the file RESUME and it gets lost with the thousand others. It should use your name - "Larkin cover letter and resume."
For resumes, key words are critical, especially if you are applying to a large company. I got this tip from someone who works at Disney: "The trick (which I learned directly from Disney HR) is that you should tweak your resume for each position you are applying to. Look at the job post and use specific words that are in the post. Before any real person reads it, the site runs a program that searches for enough keywords to deem the candidate enough of a possibility to then have the resume sent to a real HR person." Key words are key. For example, if you want to edit, list the specific programs you edit with. They search for those. This holds true at most any large companies. Many times people in HR, the gatekeepers, aren't that familiar with the exact positions. They look and search for these key words. I’ve heard the exact same about NBCUniversal at Time Warner, for example. If you apply to multiple positions at the same place, tweak your resume and cover accordingly. But be careful with that, as you can appear unfocused if you do.
I have a lot more advice in the Big List of Little Tips doc in the key doc section. http://www.gettinghollywood.com/getting-work-big-page-of-little-tips/
Very few do all this properly. If you do, you will stand out.