"I am not my thoughts." Or, as I prefer, "these thoughts are not mine." Experience that over and over again and everything gets a little easier, a little clearer. That's when the detachment from thoughts begins.
The same thing that would make me pass over a resume/cover letter for a job I'm hiring for: vagueness. The more specific and transparent a posting is, the more confidence I have in the buyer knowing what they need and who they need to achieve that goal. You get a lot of amateurs/first-timers on these sites, and that's often a recipe for misaligned expectations.
It's been years since I was on Upwork (started w/ Elance) and I felt similar frustrations. Then I signed up as a buyer, posted a job similar to the ones I was seeking, and analyzed the patterns of freelancer pitches and how the system was structured.
I started noticing missed opportunities. As a buyer, you only see the first few sentences of a proposal unless you hit the See More option. Most freelancers weren't maximizing this space. NOBODY used video. There was minimal personalization. And so on.
So I would make a personalized video for every pitch and reference it in the first sentence. Short, nothing with production or anything like that. Mostly I wanted the buyers to get a vibe for me. I'd do light research on the buyer and look at his/her feedback and reviews for other freelancers they've worked with, then I used that language to demonstrate that I had the same characteristics and skills they value the most.
This all increased my interest and close rate tremendously. I also learned which gigs to never bid on, which is a little art and a little science. You can tell by how the project descriptions are written which ones to avoid.
Hugely important for me, hiring for marketing. I need to know you can write. I need to know you can tell a story. I need to know you can be creative and seek opportunity where others don't. It amazes how many applicants either don't include one (to be fair, not all job posting sites require it) or just slap empty words on the paper and move on.
Can I plug MusicBox (http://www.mymusicbox.me/) real quick? We curate killer songs from the best indie artists and send them (for free) to a list of over 10k. We work directly with the artists and indie labels, so no issues. We want to support them, not screw 'em.