I focus on job posts by people in the US and emphasize my almost 2 decade experience in web development, my location (California), and my reliability. Clients in the US often prefer freelancers in the US because they've been burned by overseas devs before. I also mostly apply to jobs that aren't that easy to people with less experience (so I avoid any Wordpress/Joomla/Magento jobs, or any of the "convert PSD to HTML" jobs). It always helps to read the job posting entirely and ask clarifying questions in the proposal (shows that you've read it). Also, try to customize your proposal to each client as much as possible.