As a native English speaker, besides my ability to, um, deliver the work, my number 1 advantage is *nuanced communication*.
So the priority is being communicative and responding to messages at all hours. That means email, iMessage, and even phone calls when something is time-sensitive for you.
I work in weekly milestones, which means my clients don't find themselves risking a large sum of money and wondering if they're going to get a return on their investment. You pay for a week up-front, I send you nightly updates about the day's progress (and my plan for the next day), and so long as the project is moving forward quickly, then you keep investing in the next weekly milestone. That protects clients and that protects developers like me.