I have always gotten a response to a proposal whenever I write one that is very tailored to their requirements. The client wants to know that you actually read their post, understand what needs to be done, and can even provide some examples of past work that is similar to what they're looking for. That is what always works for me. Copying and pasting a cover letter in each job will get you nowhere. It helps to be on the other side of the hiring process too. I have hired people on Upwork before and know what it's like to get a bunch of applicants that obviously just copied and pasted some cover letter on the proposal. I had no confidence that they would be able to do the work because of that. So I ended up choosing someone who actually read my post and wrote about how they could achieve the job.
